Wiktionary
n. Abbreviation of uranium-235.
Usage examples of "u-235".
An isotope discovered only four years earlier, called U-235 or actinouranium, could conceivably fire off in a self-sustaining explosion of incalculable magnitude.
But could any country produce enough pure U-235 to make bombs for use in this war?
Unless the United States could overtake the Germans, the superb Nazi war plants were likely to furnish the lunatic Fuhrer with enough U-235 bombs to wipe out the world's capitals one by one, until all governments grovelled to him.
The trouble was that the mountainous Manhattan Project had labored and brought forth only one small lethal mouse of U-235, just enough for a single bomb.
Oak Ridge extracted U-235, true-but the Hanford piles used more U-235 than they produced plutonium and Oak Ridge produced nothing but merely separated out the 7/10 of one percent of U-235 in natural uranium and "threw away" the 99%-plus of the energy which was still locked in the discarded U-238.