The two Explorer-class submarines were experimental vessels built for the Royal Navy to test a propulsion system based on the use of highly concentrated hydrogen peroxide (high-test peroxide, HTP) and diesel fuel to achieve high underwater endurance and speeds.

One of these, the Type XVII U-1407 U-boat submarine, which had been scuttled at the end of the war, was salvaged and eventually recommissioned into the Royal Navy as HMS Meteorite.

Being purely experimental craft they had no torpedo tubes or radar fitted, only one periscope and were equipped with backup diesel engines to recharge the batteries and propel them on the surface.

As well as providing experience with this type of technology, they also allowed the Royal Navy to practise against fast moving underwater targets.

[4] Other countries have since developed the concept of the non-nuclear air-independent propulsion submarine to the point where it is a safe technology albeit as an auxiliary power source to a conventional diesel-electric drive, although hydrogen peroxide has long been abandoned and liquid oxygen is generally now preferred.