Compared to the following type 87, the 81s were 4.26 metres (14.0 ft) longer, yet 5 tons lighter.[1] Their range was 180 miles shorter, but speed was 1.2 knots (2.2 km/h; 1.4 mph) faster on the surface and .5 knots (0.93 km/h; 0.58 mph) faster submerged.