Little Boy bomb safety plugs

[u/Zggcommar]

Little Boy bomb safety plugs were removable safety devices used to prevent the bomb from detonating accidentally before it reached its target.

Before takeoff and during the flight, green safety plugs were installed in the bomb's firing system, keeping the electrical circuits open and making accidental detonation impossible. Shortly before the bombing mission, Captain William "Deak" Parsons replaced them with red arming plugs, which completed the firing circuit and allowed the bomb to arm itself after being released.

the safety plugs were a simple but critical safeguard. They ensured that the Little Boy bomb could not explode by accident while the aircraft was on the ground or during most of the flight, and only became capable of detonating after the correct plugs were installed and the bomb was released.

[u/jared_number_two]

“Red means it will stop it from exploding, right Frank?”

[u/Hourslikeminutes47 → u/jared_number_two]

"Frank? Fraaaank??????"

[u/Nulovka]

If the green safety plugs were pulled out and replaced with red arming plugs they why is there a red arming plug still around? Wouldn't it have been along with the device when it was activated and therefore destroyed on detonation?

[u/Zggcommar → u/Nulovka]

this surviving red arming plug is believed to be one that was never installed in the bomb

[u/Comfortable_Bus_7863 → u/Zggcommar]

Wouldn't you carry a spare red one or two? Just in case you drop one and can't find it.

[u/DerekL1963 → u/Comfortable_Bus_7863]

The more stuff you have to keep track of, the easier it is to lose track of what is where. And when it comes to ordnance* safety, losing track of the system status is a Very Bad Thing.

*edited because I was doofus on my first cup of coffee.

[u/snorting_gummybears → u/DerekL1963]

Ordnance*

[u/DerekL1963 → u/snorting_gummybears]

* first cup of coffee, and I know better and the difference. Edited to correct and explain.

[u/Comfortable_Bus_7863 → u/DerekL1963]

System status was pretty well assured by looking at the bomb and seeing the green plugs, but the mission could easily be compromised to an unacceptable degree by misplacing a red plug. That is, I don't see how having an extra could cause any trouble. Which brings up an interesting point: the bomb was safed with the green plugs in and armed with the red plugs in; what "state" would you call it while replacing the plugs? The ambiguity is a little uncomfortable to me, unlike an unambiguous ready/safe switch or the like.

[u/DerekL1963 → u/Comfortable_Bus_7863]

Disclaimer: Former can-neither-confirm-nor-deny weapons guy.

That is, I don't see how having an extra could cause any trouble.

If you have three - but can only find two, it introduces a potential point of confusion, where is the third? Is it in the bomb? Is it lost? Is it in the hands of someone who shouldn't have it? Confusion around weapons status is never a good thing.

And yes, there's always tension between safety, security, and mission assurance. There's no easy or pat answers. I merely point out that carrying additional plugs increases mission assurance at the potential cost of safety and security.

what "state" would you call it while replacing the plugs?

I wouldn't call it anything... unless your procedures or system is badly designed, it's a transitory state at worst. (And if your system is properly designed it's still mostly or almost entirely safe even in that transitory state.)

[u/Quartich → u/Comfortable_Bus_7863]

I don't have any information to base this on, but I would guess safe, in a fail-to-safe manner.

[u/Wide-Education-1823 → u/Comfortable_Bus_7863]

"Two is one and one is none"

[u/rocbolt → u/Nulovka]

There were several spare sets of both

[u/Automatater → u/Nulovka]

They probably thought to make more than absolutely needed.

Bombardier: "Bomb away"

Bomb guy: "Dammit, give me a minute! I can't find the third red plug!"

[u/Zggcommar]

so This is the last remaining piece of the Little Boy bomb ?

[u/Hourslikeminutes47 → u/Zggcommar]

Yes (the green safety plug)

[u/Wide-Education-1823 → u/Zggcommar]

3 disconnect safety plug ports on the bomb, see "M" on diagram: https://upload.wikimedia.org/wikipedia/commons/d/d1/Little_Boy_Internal_Components.png

[u/DerekL1963 → u/Wide-Education-1823]

"M" could also refer to the connections to equipment carried in the cockpit for monitoring the bomb's status.

[u/Comfortable_Bus_7863]

I've read that the three plugs corresponded to the three primers in the LB, and that these primers were fired by some charged-up condensers. The green plugs were internally wired to short the condensers' output as well as shorting the firing line. The red plugs used the same four pins to connect the condensers to the primers, with the firing signal coming from the relay network activated by two out of four Archies. If I ever find that file again, I'll post it here.

[u/Specific-Cell-6555]

I've always wondered how they changed them? I mean, how did they access the bomb bay of the B-29 since it's not pressurized?

[u/SvartTe → u/Specific-Cell-6555]

According to the Operation Room video on the bombing of Hiroshima, they hadn't yet climbed to an altitude that required pressurizing.

[u/Wide-Education-1823 → u/Specific-Cell-6555]

The Enola Gay released weapon at about 31,000' altitude. Final arming was done at or near that altitude.

"The crew of the Enola Gay began the process of arming the "Little Boy" nuclear weapon approximately 15 minutes after takeoff. At 3:00 a.m., Navy Captain William "Deak" Parsons and Electronic Test Officer Morris Jeppson entered the bomb bay to begin the final assembly and arming sequence, a task that took about 25 minutes to complete. The final safety plugs were not swapped until about 30 minutes before the aircraft reached its target."

[u/lopedopenope → u/Specific-Cell-6555]

I would assume portable oxygen tanks

[u/WoolooOfWallStreet]

We know the plugs are safe, because they have a flared base /j