The "Collins" class is an enlarged version of the "Västergötland"-class submarine designed by Kockums. At in length, with a beam of and a waterline depth of , displacing 3,051 tonnes when surfaced, and 3,353 tonnes when submerged, they are the largest conventionally powered submarines in the world. The hull is constructed from high-tensile micro-alloy steel, and are covered in a skin of anechoic tiles to minimise detection by sonar. The depth that they can dive to is classified: most sources claim that it is over .