Marines lowering the US and Marine flags over brigade headquarters in Mogadishu yesterday. Six Cobra helicopters swooped low as the last few dozen troops from a force that at its height reached 28,000 headed towards four warships lying offshore. 'See ya. We're outta here. We accomplished our mission,' said one officer. The withdrawal leaves a depleted UN force to deal with a country with no government, bedevilled by banditry and ravaged by cholera.