[3] John P. Gaines was powered by two oil-fired boilers and a single 2,500 hp (1,864 kW) vertical type, triple-expansion reciprocating steam engine.

Crew accommodations were provided in a large three-deck superstructure located in the middle of the ship (medium blue in the picture) directly above the machinery space, and in a small superstructure (medium blue in the picture) located at the stern.

The bridge, radio room and Captain's quarters were on the top deck (yellow in the picture) of the three-deck structure.

When the ship was armed, the gun 'tubs' (white in the picture) were located at the bow, stern and above the bridge.

Steam-powered generators provided electric power for radios, navigation equipment, refrigeration compressors, pumps, lighting, and degaussing.