Ft. Drum is 350 feet long, 144 ft wide, and with its top deck 40 ft above the mean low water mark. Its exterior walls are between 25 to 36 ft in places.

It was equipped with 14in guns in armored turrets - the only armored turrets in Manila Bay. It had 4 casemated 6in guns for immediate self-defense.

Drum was amply supplied with rations, but it did not have sufficient drinking water.  It nonetheless kept firing until the surrender, despite being constantly hit.