 Complete the following phrase:  Historically many jet trainers were marketed with specialised attack variants e.g. the BAC Jet ProvostBAC Strikemaster and the Cessna T-37 TweetA-37 Dragonfly. Especially against opponents operating without a fighter screen or an effective anti-aircraft capability, such trainer derived attack aircraft could perform adequately. For example, Impala aircraft derived from the Aermacchi MB-326 trainer formed the main strike strength of the South African Air Force in its 