sentences:  The Type 99 Mark 1 Fixed Model 3 could be equipped with a 100-round drum, but the size of the drum was itself a problem in fighter installations, although the Model 3 guns were installed on the initial production versions of the A6M3.A more practical solution was provided by the Type 99 Mark 1 Fixed Model 4, which featured a Kawamura-developed belt feed mechanism.The Type 99 Mark 2 was a heavier weapon with a stronger recoil, and was not put in use by the IJN before 1942.