This new phenomena [atomic energy] would also lead to the construction of bombs.... A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port, together with some of the surrounding territory. However, such bombs might very well prove to be too heavy for transportation by air.

Letter to President Franklin D. Roosevelt [August 2, 1939] (the letter that resulted in the assignment of government funds for developing the atom bomb)