http://www.netrover.com/~timt/cheats/g/gravityforce.html (Amiga Plus Extra No. 5/97, 05/1997)
05 --- AGNUS | 20 - REACTOR | 35 -- PALACE
10 -- PARSEC | 25 -- VISION | 40 --- ALIEN
15 - CRYSTAL | 30 --- ORBIT | 45 -- FALCON
Instead of the normal level codes enter "WARPnn". Substitute a level number for 'nn' to start there.