Operation Blockade seems to be the unofficial sequel to Infogrames’ earlier
Beach Head 2002 as it’s quite similar. The only exception: here, you shoot at
ships, planes and soldiers – and in the other game, you shoot at tanks, planes
and soldiers.

You are a lone gunner on some island in the Pacific (or somewhere else) and
need to get rid of all attackers. To accomplish this, you have some big guns
at your disposal – among others, an assault rifle against walking cannon
fodder, an anti-air gun against enemy planes and a mortar against ships. You
cannot move (it’s a gun, not a tank) but you can rotate 360 degrees so you
always can follow the enemy. You have only one life; if you die, the game is
over. The ammunition is limited too.