April 15, 1943. Oppenheimer and Serber are trying to brief all of the scientists on what they're there to do, which is "produce a practical military weapon in the form of a bomb in which the energy is released by fast-neutron chain reaction." That description just sucks the life out of what they're doing, doesn't it?
During the briefing, Oppie becomes worried about all of the workers (electricians, plumbers and so on revamping the school for their use) hearing Serber say the word "bomb" over and over again, so he starts referring to it as the "gadget," and the nickname sticks.
Over the next few weeks there are many more briefings. Basically, Fermi's experiment worked, but now they need to make it a bigger/faster chain reaction to produce more energy, and it has to be much smaller and light enough to travel by airplane. This is no easy feat, physics nubes.
They already have the basic theoretical design planned out. They call it the "gun assembly method," because it resembles an adapted artillery gun. Inside the gun barrel they will fire one piece of uranium at the other, forming a critical mass when the pieces hit. Surrounding the uranium will be a tamper to keep the neutrons from escaping, and thus make the explosion even bigger. But there are still a ton of questions about how to make this method work.
Unfortunately, Los Alamos is in shambles due to all the renovations that are necessary to make the grounds fit for their purposes. Married couples are stuck sleeping on bunks like it's summer camp, bathing facilities are very limited, and it's clear that they'll all be pretty isolated together.
They all work at the Tech Area, where only scientists are admitted with photo IDs.
The security around Oppenheimer is even more extreme, but it isn't just for his safety—the government still wasn't sure whether Oppie is a Commie rat or not, so he's being watched to make sure he isn't a Soviet spy.