Attempts to resolve this resulted in both improved new ship designs and in modifications to existing ships. AA weapons were improved in number, power and fire control, with some classes equipped with main armament capable of AA use, even at the expense of reduced calibre. Secondary armament progressed from largely ineffective batteries of machine-guns and 2 pdr "pom-pom"s to Bofors and Oerlikon rapid-fire cannon, sometimes at the expense of torpedo tubes. Some classes were fitted with a single AA gun, but this was unsatisfactory and discontinued. Effectiveness was further improved by improvements in fire control, such as the adoption of the Dutch Hazemeyer system.