 Complete the following phrase:  The first large-scale testing of the rocket launchers took place at the end of 1938, when 233 rounds of various types were used. A salvo of rockets could completely straddle a target at a range of . But the artillery branch was not fond of the Katyusha, because it took up to 50 minutes to load and fire 24 rounds, while a conventional howitzer could fire 95 to 150 rounds in the same time. Testing with various rockets was conducted through 1940, and the BM-13-16 with launch rails for sixteen rockets was authorized for production. Only forty launchers were built before 