This is another superb offering from the desk of Randy Sanders.  As the hull thickness is considerable, this model can easily be scaled down and still retain adequate strength. 
 
The Sjöormen class (Sea serpent) was a class of submarines built for the Swedish Navy in the late 1960s. They had a teardrop hull shape and were capable of diving to 150 metres (490 ft). At the time of their deployment they were regarded as one of the most advanced non-nuclear submarine classes in the world, incorporating many new features including an x-rudder and anechoic tiles.[1] Both speed and underwater endurance were at the time very high for a conventional submarine. The submarines were retired by Sweden in the early 1990s. In the late 1990s, all five submarines were acquired by the Republic of Singapore Navy (RSN) and four were relaunched as the Challenger class following modernisation and tropicalisation. 
 
Length as offered: 1062.5mm
Beam as offered: 126.7mm
Volume: 1730cm3
Filament required: 1.73kg (2 rolls)
Hull wall thickness: 3.5mm
 
As this boat has x-tail control surfaces, it will be a superb performer in terms of pitch and yaw performance, making it well-suited for use in a pool or other smaller body of water.

Recommended material for RC use: ABS, ABS-GF, ASA, ASA-CF, PETG
Largest z-axis height: 235mm in supplied scale