The Hai (shark) was an advanced model of the Marder

Marder (midget submarine)

The Marder was a German miniature submarine developed from the Neger. The craft was 8.3 metres long and unlike the Neger included a flooding tank in the nose allowing it to dive. Another improvement was the dome through which the pilot viewed the outside world that also served as the craft’s...

-class midget submarine

Midget submarine

A midget submarine is any submarine under 150 tons, typically operated by a crew of one or two but sometimes up to 6 or 8, with little or no on-board living accommodation...

s created in Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 during World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 and operated by the K-Verband

K-Verband

The K-Verband was a World War II German naval unit that operated a mixture of Midget submarines and explosive speed boats....

. Its prototype performed poorly during test runs and therefore no other boats were produced.

The Hai was thirty-six meters long and its length allowed for larger batteries, giving it the maximum speed of twenty knots under water. In addition, the Hai could remain under water for up to two hours.