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The shells were able to penetrate more than 4 metres (13 ft) of reinforced concrete, but had low muzzle velocity, and as such were very inaccurate: 36 m (118 ft) on 1,000 m (3,300 ft) range. As a result, they saw very limited use during World War II; only about 200 shells were ever fired.
They were regarded as a secret German weapon, and there is speculation that the limited use was in order to reduce the chance of dud shells being captured and exploited by the Allied forces. A more likely reason, however, is the poor accuracy of the shells. 
- Les étranges obus du fort de Neufchâteau (French)
- War and Games. "V 3 – THE HIGH-PRESSURE PUMP GUN". http://warandgame.wordpress.com/2009/07/13/v-3-the-high-pressure-pump-gun/. Retrieved 2009-12-15.