Russian submarine Pochtovy

The boat was designed by Drzewiecki and built at the Metal Works St Petersburg in 1908.

[1] The primary objective of the design was to equip the submarine with a sole diesel propulsion system for use both when surfaced and submerged.

Forty-five cylinders containing 350 cubic feet (9.9 m3) of air at 2500 psi could give the boat a 28-nautical-mile (52 km) submerged range on one engine.

The exhaust gases were vented via perforated pipe under the keel.

The system proved reliable in trials but condensation problems and the tell-tale wake produced by the exhaust resulted in no further development and the boat was stricken in 1913.