From Worms Knowledge Base
In Worms and Worms United for MS-DOS, holding down both F1 and F3 at the same time long enough for the weapon name to flicker between the various weapons, and then tapping space makes your worm fire a hybrid of the Bazooka and Uzi weapons - a rapid-fire weapon like an Uzi which fires Bazooka missiles at full speed, each doing a potential 45hp damage. While it is possible that this was a deliberate inclusion, it seems more likely that this is a glitch.
A more reliable way to trigger the glitch is to use the right click menu to select the Uzi, hold F1 and Space as you click on the Uzi. You can also use F5 instead of F1 to fire dynamite shots instead of bazooka shots, which deal more damage. The graphics for the dynamite shot are glitched and look like horizontal lines.