The one I’m thinking of is SADM, which stands for either “Special Atomic
Demolition Munition” or “Small Atomic Demolition Munition,” depending on
whom you ask. I overstated the yield by a decimal point or two, though–not
that you’d notice if the thing went off while you were trying to plant it.
The most detailed specs I have are: “0.1-1 KT – 163 pounds 39 x 26 inches –
79 pounds without case.” Seems to be still in inventory.