Delfin I (Dolphin I) underwater vehicle

The hull is made of 5-milimetre thick ST-41 sheet steel, reinforced with flat bars. Amidships there is a superstructure with a pressure hatch. Another hatch is located in the lower part of the hull, allowing for emergency evacuation. On both sides of the hull there are ballast tanks.
Four 8-litre compressed air bottles allowed for removing water from the tanks. The vessel was controlled by adjusting the length of the towing cable and by vertical and horizontal dive planes. Large, sled-shaped fins on the bottom controlled the pitch. These were used also as supports during transport and stowing of the vehicle. „Delfin I” could operate for 2 hours underwater at up to 35-metre depth.