It appears Deke Parsons armed it on the ground and the weaponeer, Fred Ashworth, pulled the safety plugs at 4 am
I wrote a review of books of this era which may be helpful
In The period covering the genesis and production of the first atomic bombs is well served by literature. The initial British efforts are elegantly described in three books by Margaret Gowing, the official description of the US efforts were covered by Hewlett and Anderson in The New World and this was updated by Richard Rhodes' magisterial The Making of The Atomic Bomb which rightly won the Pulitzer Prize.
In The Manhattan Project Stephen Groueff covered the industrial problems in a most accessible book and I found Stalin and the Bomb by David Holloway most rewarding.
The later US developments were covered by U.S. Nuclear Weapons: The Secret History by Chuck Hansen