Complex sentence: In Port Sudan there were six Gloster Gladiator biplane fighters flying trade protection and anti-submarine patrols over the Red Sea, responsible for air defence of Port Sudan, Atbara and Khartoum and close support of land forces.
Split into simpler sentences: In Port Sudan there were six Gloster Gladiator biplane fighters. The air force's role in Sudan covered shipping protection in the Red Sea (including anti-submarine patrols), air defence of Port Sudan, Atbara and Khartoum as well as close support for land forces.