Rapid motor refurb helps put WWII sub back in the water

When the team from the UK television programme Salvage Squad took on the challenge of restoring one of the few remaining German "Biber" one-man submarines from the Second World War, one of its tasks was to revive a 60-year-old 500V DC motor that would propel the vessel when it was submerged.

To minimise the submarine`s size and weight, the motor had an unusual design, including an armature with commutator bars flat to the end of its winding coils, rather than the usual cylindrical shape. The brushgear ran flat to the commutator face.

Although the Squad had three months to complete the restoration, it allowed the specialist motor repairer Wyko EMS just 48 hours to test and overhaul the machine.

When the motor arrived at Wyko`s Gosport branch at 9am on a Monday morning, it was dismantled immediately and the armature and field frame coils were steam-cleaned. Claire Barratt (above), a member of the Squad, arrived later that day to test the motor`s conductivity, guided by Wyko`s Terry Elsbury.

Despite the motor`s age, the tests showed that it could take power from the boat`s batteries without needing to rewind the armature or field coils. Moisture residue was removed using a stoving process, and the insulation was restored by immersing the windings in varnish.

While the coils were being treated, the brushgear was dismantled, re-insulated and coated with an anti-tracking paint, and new carbon brushes were fitted. Following successful rotation tests on the Tuesday morning, the motor was returned to the Royal Navy`s repairer, FSL, to be re-installed in the submarine.

As viewers of the resulting TV programme, shown in the UK earlier this month, will have seen, the vessel was re-launched successfully (above), watched by a former Biber pilot, Heinz Hubler. The revitalised motor was used to propel the vessel both on top of, and under, the water because it was felt that the internal combustion engine originally used for surface manoeuvres was potentially hazardous. The submarine will now be displayed at the Royal Navy Submarine Museum at Gosport.