The Jymy-class motor torpedo boats (English: "Rumble") or J class was an Italian-designed and built class of motor torpedo boats, seeing service during World War II with the Royal Italian Navy and later with the Finnish Navy.

The four boats of the J class were built by Cantieri Baglietto in Genoa, Italy and purchased by the Finns on 5 June 1943.

Following World War II, the vessels were rearmed according to the Paris Peace Treaty of 1947, losing their torpedo capabilities and given more guns.

[1][2] All four vessels were constructed in Italy and served with the Royal Italian Navy during World War II.

[4] Their maximum speed was reduced to 35 knots (65 km/h; 40 mph) and their displacement decreased to 22 tonnes (22 long tons).