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Larry DeCuir’s Interview

Manhattan Project Locations:

Larry DeCuir served in the 509th Composite Group during World War II. In this interview, he discusses his experience being stationed on Tinian Island during the war and working on the X unit of the Fat Man bomb, which was designed to trigger the bomb. He also reflects on the level of secrecy involved in the Manhattan Project. DeCuir describes the housing on Tinian, and recalls witnessing the B-29 planes take off from Tinian airfield for missions over Japan.

Date of Interview:
February 22, 2017
Location of the Interview:


Cindy Kelly:  I’m Cindy Kelly, Atomic Heritage Foundation. This is Wednesday, February 22, 2017. We’re in Encino, California, and I have with me Larry DeCuir. I first want you to tell me your full name and spell it, please.

Larry DeCuir: Laurence Edwin DeCuir. L-A-U-R-E-N-C-E, Edwin is E-D-W-I-N, and DeCuir is D-E-C-U-I-R. It translates to “of leather” in French. If you go to Montreal, you’ll see a lot of shops with my name on the window. I don’t own those shops. They handle leather.

Kelly:  Great. Larry, tell us when you were born and where.

DeCuir: I was born on May 2, 1922 in Sacramento, California. My father and mother had both moved from Louisiana to California. It was, in a sense, a promised land for people in Louisiana, who had come on hard times. In the area where they were in Louisiana, it was part of the Louisiana Purchase. If you look at a map of Louisiana when that was purchased from Napoleon, you will see that a portion of the area of the river was assigned to my ancestors, same last name, DeCuir. 

Anyway, they lived on the east bank of the Mississippi, but that whole area came on hard times. A large contingent of them and the Porshays moved to California. There is a large contingent of them there now.

I was born in Sacramento, and I grew up there. I graduated high school there. I went to two years of junior college. I will never forget, there was an entertainment program at Sacramento Junior College on December 7, 1941, and there was a Japanese girl singing. Her performance was stopped, and the announcement was made that the Japanese had just bombed Pearl Harbor. She gulped a few times, and went on singing as beautiful as ever. I’ll never forget that. It was quite a moving experience.

Of course, things proceeded from there. We all had to join the military reserve or something, and I completed through two years of UC Berkeley when I was called into active duty. The option for Army Air Corps—which it was then, it wasn’t Air Force yet—the option that I wanted to participate in was communications. I had to switch from there to engineering, and then I got, fortunately, back to communications.

My first assignment was Boca Raton, Florida, from which I went to Yale University; I got a certificate from there. I went to Harvard; I got a certificate from there. I went to MIT; I got a certificate from there. I went to Great Bend, Kansas, from which I was assigned to Puerto Rico to set up a 1st and 2nd echelon airborne radar maintenance facility for the planes that were flying from the Middle West to Puerto Rico, which is approximately the same distance as from Tinian to Japan.

They were, in a sense, going out there with good training.

I happened to be in the area where we were servicing these planes if they needed it. Most of them were in quite good shape. A lieutenant colonel came from Great Bend and looked over what I had going there and told me that he was going to take it over, and I should go back to Great Bend, which I did. “Yes, sir, no, sir, no excuse, sir.”

When I got back there, the administrative officer, who was the best person to get to know in the organization, told me they were looking for people who could do what I had done at Wendover, Utah. “You want to go?” He said otherwise he didn’t have any place to put me.

I said, “Well, I’ll go. Let’s get this over with. I want my college degree.”

I went to Wendover, hitchhiking from Great Bend in the middle of winter, riding with some very kind people who picked me up by the side of the road, covered with snow.

Things progressed from there. I was able to fit in the organization and prepare to go to Tinian with the group to complete the mission. I was flown out there. As I indicated earlier, the best meal I ever had in my life, even to this day, and I’m ninety-four years old, was on Christmas Island in the Marianas group. There was a sergeant there who put on the best meal possible. I don’t know how anybody could ever exceed any aspect of it.

We went on out to Tinian and did the job, and came home in a troop ship, triple-bunk troop ship, instead of flying back in a C-54. That was the biggest disappointment I experienced in the military was going back on a three-deck troop ship, three-bunk troop ship.

Security was one of the most difficult and, in my view, unpleasant aspects of the whole experience. After we showed that we could do the whole job in Wendover, we flew out to Tinian. I kept looking for some evidence of the Japanese who had owned the island. They still owned an island called Rota, just south of Tinian, but it was occupied. They never bothered to take the island away from the Japanese. They said, “Somebody might swim over at night to try to do some damage.” But I saw absolutely no evidence of that, nor did I hear of any.

In the process of preparing for the strike on Japan, the airplane crews flew a lot of missions with what they called “pumpkins,” which were large bombs, the same size as the Nagasaki bomb, but they just had high explosive in them. They flew lot of those. They flew them over Japanese-held islands, and were fired on by anti-aircraft. I remember hearing them complain that this was tough duty, really. The nuclear weapon targets, they flew in very high. There were a few planes, and they didn’t have the opposition that they did on the other islands around the Pacific. We just did our job, and they took us home in a three-deck troop ship, which was very disappointing. The chow was terrible. Other than that, I was very happy to get home.

Kelly:  Let’s start back at Wendover, because there are still barracks standing there. Do you remember where you lived?

DeCuir: I was in the BOQ [bachelor officers quarters]. I could go to that place now, but who needs it? It’s there. I don’t know what they use it for. We went with the 509th reunion group back to Wendover, but we never got near the barracks that are still there. We were all out on the runway and talking to Colonel [Paul] Tibbets’ son, and going through the social events and whatnot.

I don’t know what condition it’s in now, but it was, it was a thriving base. I know I had to corral my enlisted men. They always wanted to go across the border to Nevada and participate in the gaming joints. I mean, it was almost a walk across the border from where we were to Wendover, Nevada.

Kelly:  You’re saying that was allowed, or not allowed?

DeCuir: Oh, it was allowed. As long as they showed up for work and did their job, well, their time off is their time. Never had any problems with any of it. We packed up and went over and did the job and came back.

Kelly:  What exactly were you doing on Wendover?

DeCuir: I was responsible for the fusing of the Nagasaki bomb. My job was to get the equipment, to check it out, to set up the harness for the large number of fuses. The Nagasaki bomb was a sphere, and the reaction was accomplished by an implosion wave that compressed the plutonium in the center of the sphere as small as possible, injecting slow neutrons into the process, which caused the plutonium to fission, which means that it would split apart. When the atom splits apart, large quantities of energy are released. We set it up so the whole thing would go at once instead of a number of different explosions, it was all one big explosion.

What it amounted to was when the bomb got far enough in its trajectory from the plane, then the fusing system would be charged up and ready for the last signal from the ground as to how high up it was to go off. When it went off, it took everything with it. 

We used—well, you could call it radar. It’s absolute altimeter is what it was, amounted to. When we got far enough above the ground, or low enough to the ground, then the fusion [misspoke: fission] process occurred, which released large quantities of energy and blew everything to pieces. That was it.

I had one of three Quonset huts on the south shore of Tinian, where the planes come down the runway and drop and go off to Japan. I just had this one Quonset hut.

We prepared the harness for the bomb. The bomb is spherical in shape, and there are detonators all around the sphere. We had this large device, which they called the X unit. Through aircraft spark plugs around the rim, we guaranteed that every detonator went off at the exact instant. When I say instant, I mean within microseconds of each other. There was a perfect spherical wave compressing the plutonium. At a stage in this compression, then the slow neutrons were introduced into the process, which caused the plutonium to fission, and it released energy plus particles. The energy which it released did the damage.

That’s what we did. We were ready to go. There were three nuclear weapons. The first one was U-235, which was on—what was the target? It was—

Kelly:  Hiroshima?

DeCuir: Yeah. Then the next one was on Nagasaki. The third one was in the Truk Islands [misspoke: Bikini Atoll], where the Navy wanted to determine what would happen to a large contingent of naval vessels with the atomic bomb dropping on them. They conducted that test. 

Kelly:  That third bombing was after the war?

DeCuir: Yes, yes, absolutely.

Kelly:  How long did you stay on Tinian?

DeCuir: Until they put us on the troop ship. It wasn’t that long, because there’s no reason for us to stay, because we were there until Japan surrendered. Turn off all the guns, so there was no more fighting. They’re not going to put us in good quarters there, eat high and all this. Troop ships, three men into a bunk, come back, get off at Oakland, go by train to, I think, New Mexico. You know, we did the job, and goodbye. I’m happy to say goodbye.

I didn’t have any interaction with any of the technical aspects of the reaction, the nuclear reaction. I just set it off, that’s all. Set it off, which causes the plutonium to compress in the presence of slow neutrons. Anyway, that’s all.

They let us go. I was happy to say bye-bye, sayonara, or whatever. That’s all. Anything else?

Kelly:  Were you ever worried that this very complex bomb that had to be imploded—

DeCuir: No, never.

Kelly:  —within microseconds wasn’t going to work?

DeCuir: No, not, not the slightest.

Kelly:  You were confident?

DeCuir: Absolutely. I had to control the detonation equipment, so what’s to worry? It takes this spherical compression wave to do it. You have to have all these detonators spaced exactly the right amount, and spaced and set off within microseconds of each other.

The pilots that flew out and dropped dummy Nagasaki bombs, they said they were shooting at them. They wanted to bring them down. The ack-ack was coming after them. They were complaining bitterly, the pilots were, in the officers’ club after they got back from a mission. He said, “Boy, they want to bring us down.” I mean, war is hell. What do you expect?

We were protected where we were in that the Marines were there, and nobody could invade the island. But again, that is still the largest airfield in the world, to the best of my knowledge, on Tinian in the Marianas group. They would be flying out of there for two, three hours, B-29 after B-29 loaded. We are up here in a tent, and we’re looking out here. Here’s the runway coming down here and it drops into a little canyon, sort of, and off they go. There’s no sleeping that night, none whatsoever.

You could see them. They would be smoking cigars, a lot of the pilots of the planes. You couldn’t wave, they couldn’t see you, but it was quite an adventure. They would go out, boy, hundreds of B-29s. 

But boy, when they come out of there, there’s no sleeping, I’ll tell you, on the whole island, when they go off to Japan. But, that’s war. We ended it, fortunately.

Kelly:  Tell us some more about the security that you experienced.

DeCuir: Everybody I associated with was cleared. The tight-lipped security was away from the island. But in Wendover, it was very tight.

We had a fellow in our crew who was working on the mechanics of setting off the bomb, who had gone to a bar in, I don’t know, southern California. He had mentioned in the bar that he was working on something that would end the war. He never came back to Wendover, and the next thing we heard he was in Alaska and he was not about to get out of Alaska. He was in the Aleutian Islands, because somebody had heard him speaking in that manner in the bar. Our commander was very careful to call that to your attention of every person in the organization. “Just be careful. You don’t know what you’re working on, you have a narrow job. Stick to that, don’t speculate.”

I remember once a guy was in Roswell, or maybe it was in Los Alamos, or Wendover. There was a lot of speculation among the air crew. They didn’t know—that’s what I heard—they didn’t know what it was. One of the fellows in the flight crew said to me, “I know what it is.” He said, “It’s an atom bomb.”

I just looked at him, and I was thinking of this guy who disappeared and went to Alaska, and I said, “Oops.” How do I softly get out of this? I said, “That’s a very interesting speculation.” I remember what I said, “That’s a very interesting speculation.” I didn’t want to lie. I said, “We’ll just have to wait and see, won’t we?”

He said he thought he’d surprise it out of me, but he didn’t.  That was, that was all that was said. I don’t know if anybody got to him. For him to even ask that is, is very shaky ground. He never talked to me about it afterwards again, and I never said it to anybody.

The most shocking, difficult thing that I experienced in the whole period was transport planes flying in with American newspapers with headlines saying, “Atom Bomb Dropped on Japan.” I said, “No, I can’t look. They’ll send me to Alaska.” You just don’t know.

See, it’s such a change like that. “Here, here’s the newspapers, here, read it in the headlines, ‘Atom Bomb, Nuclear Weapons,’” this and that. It took a while. I think after a couple, three days, we got over the shock effect and we could talk about it calmly.

Boy, the security was—I don’t expect I ever will see anything like that again. Because you can’t keep communication constrained like this. Let alone the Internet, but everybody knows everything all around the world now. You can’t hide it. 

I read a book on the PT boats with [President John F.] Kennedy and the experiences he had with them. We were winning the war. There’s just no question about it. That’s my personal opinion. I think they, they were ready to give almost, except the diehard warlords who wanted to control the Southeast Asia, including Australia. They wanted the whole country of Australia be under their rule. However, we thwarted their efforts. We now are friends like this.

I wear something I know that we got from Japan. Things change, fortunately and often for the better.

Kelly:  Have you been to Japan?

DeCuir: Never. When my wife was alive, we used to travel. We went to Europe a lot, and we went to North Africa. We went to South America, we went to Panama Canal, Canada, Alaska, all over. But not Japan. I read about it, and that’s enough for me. I would expect if you go over there, you would see the results of war. I mean, they took such a pounding that it would take them decades to get over it, to return their country to a semblance of what you might call normalcy. Though I believe they have recovered quite remarkably, and they are one of our major partners in the Pacific as we speak.

If you were to point at anybody, it would be the people who wanted to conquer the whole Pacific, Australia, New Zealand, all the other islands, the Hawaiian Islands, the Philippines. It didn’t work out that way. In my view, we would have beat them whether we had the atom bomb or not. That’s my personal view, in reading about it and all that kind of stuff.

I was very happy to be able to play the part that I did. I was never in jeopardy at any time. I went out in a C-54, ate the best meal I ever ate in my life, came back on a troop carrier, three-deck. I was in the middle deck, if you can believe it. They dumped me off in Oakland and shipped me to San Francisco and discharged me, because I didn’t want to stay in. We did the job. It’s over. I had to get my college degree.

Kelly:  No band playing at the docks?

DeCuir: Nothing, none whatsoever. Well, who needs it? You do a job, you expect the people to say, “Attaboy.” So you got something else to do. You never are still. The area where they acknowledge what you have done, you always have to go on to something else, hopefully better.

Kelly:  One question is about your liaison. You had a liaison between the military and civilians, is that right?

DeCuir: We were all in the same organization. The military were additional hands assigned to the civilians. The civilians ran the show. The civilians, especially on the—what I worked on was called the X unit, but it’s really the fusing for the Nagasaki bomb. It was designed and built by Raytheon in Waltham, Massachusetts. Those guys from Los Alamos were interacting with them every day almost. I mean, if they had a question, they would consult with their peer counterparts in Raytheon and they would tell me what to do. I would say, “Yes, sir.” It was pretty well established exactly how status would be assessed and progress would be made. It worked good.

I never had a shot fired at me. But those pilots who flew what they called pumpkins, those huge bombs that were like the Nagasaki bomb in size, but they dropped high explosive. They really took some scary missions, because the anti-aircraft, they were trying to bring them down. 

The only shot fired at me—it wasn’t fired at me, that came close to me—was on a firing range in Florida, where we were cadets, before I went off to Yale. They have these revetments, they’re triangular shape rows of earth. They would put a target on one side and candidates, soldiers would fire at the targets. Then after the guy running the operation said, “Cease fire,” they all ceased firing, except this one time. Behind the revetment that I was working over to pace up the targets, there was somebody a good deal distance away and a bullet came whistling by my head. I dropped, but it was too late then.

I talked to the sergeant and he said, “Oh, somebody over there is firing in a random direction. They shouldn’t do that.” Of course they shouldn’t, especially if I’m there, no helmet, nothing, open, and goes by my ear. I’ll never forget that. That’s as close as I ever came to experiencing a mishap in the military. But it was just accidental, I mean, it could happen anywhere. If you’re out in the woods hunting, it could happen to you. He said that the plebe or whatever, he was just firing randomly into the air. He shouldn’t do that, he’s told not to do that.

Then I did read that in preparing troops for Germany, I guess, or trench warfare, whatever they would call it, they would have guys crawl along the ground with live fire above them, and some of them would actually get killed in that training. I said, “Please don’t send me to the infantry, please, please.” I passed muster to stay on that assignment, for which I was very glad.

But I almost was in there when this bullet came by my head. If it had hit me, there’s no doubt to me it would have taken me out. If I had recovered, I wouldn’t be the same at all. That’s the only time I was ever in real danger, what I would say real danger.

Kelly:  It sounded, from the write-up I read about your tent, that you and one of your buddies—

DeCuir: Leon Smith, who just died a couple of months ago, yeah.

Kelly:  Tell us about that.

DeCuir: We got on Tinian and everybody was in—you’ve seen the pictures in there of all these guys mobbed into the Quonset huts. We didn’t want to live like that if we could help it. This lieutenant—I don’t know what he would be now—Smith, said, “Look at these old packing crates. There are sides there, why don’t we see if we can make something with this?” So, we did. [Philip] Barnes, [Morris] Jeppson, Smith and I, we got together and we put the footing in and put these crate sides in for floors.

We had the best quarters for the whole organization, really. Everybody else was on concrete. We had floors that had give. It was really, really nice. There wasn’t any danger. There wasn’t any danger of any sort from anybody. 

Actually, I read a book just recently that said that [General Curtis] LeMay did more damage than the nuclear weapons, really. Because he had blanketed the island [Japan] from coast to coast, north to south.

He had just taken them out. He came around to look at our installation, and he had a line that he kept repeating. He said, “I see it, but I don’t believe it.” That was just for the press or whatever. To distinguish the nuclear weapon damage—this is what I’ve read subsequently—from the other damage was difficult, actually. Unless you had a Geiger counter, then you could tell it was—but the explosions, the burning, all that kind of stuff, the conventional weapons did the same thing.

I read a lot political about all this. The position that I get from a number of authors is that we gave them an excuse. The warlords didn’t want to give up, but the Emperor says, “Enough. That’s the end. We’re done.” Now, they’re going to obey the Emperor, or not? Well, you know, they don’t have much choice, really.

But in this last book which I read, which was within the last year, it talked about all the damage that LeMay and—I forget the name of the Air Force—but he had, he had practically destroyed them. When he came around to look at this little Quonset hut, or this little thing was going to do all this, I “I see it, yeah, yeah, okay, okay.” But he had done the work, so in evaluating the damage, it’s hard to determine what was high explosive as against nuclear, except to check the radiation. The damage was very, very similar.

A boyhood friend of mine from grammar school was on Okinawa at that time. Actually, he was in the Seabee, Marines. He told me about it afterwards, that the bomber [Bockscar] that dropped the bomb on Nagasaki was low on gas, had to land on Okinawa, which is just off the coast of Japan, to refuel, because their fueling system was not functioning properly. He said, yeah, he was there, the plane came in and they refilled it with fuel and off it went. That was in Nagasaki, and we grew up in Sacramento, California. It was quite an experience.

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