I have no doubt these engineers were smarter than myself, but I am struggling to understand how that was the best solution at hand. For something that weighs 7300 kgs, how was there not sufficient space to include a heater and battery? Now your military base needs to maintain both the nukes + a chicken coop.

For a crappy back of the envelope calculation: a human outputs 100 watts and is 70kg. A chicken is 2kg, so by rough ratios, you would expect a chicken to to be a 3 watt equivalent. A quick search is indicating a (modern) car battery is 600 watt hours, meaning we could fuel our chicken-equivalent-heater for eight days.

It was 1950's era tech... perhaps they were concerned about the acid leaking and damaging the mines, or hydrogen sulfide gas building up inside the casing.