Testimer? Battleship hidden in a gas giant. Very pulp fiction

[TPOT]

All I can remember is I read this in the 80's. Plot was a prisoner was sent to find a warship hidden in a gas giant, and he had a 1 shot pistol in his index finger, that when he used it, blew the end of his finger off. The testimer from the thread title was the group that hid the ship. Not sure if that is correct.

 

[PaulMmn]

Timothy Zahn wrote "COBRA--" which included a group of soldiers modified with weaponry-- Our Hero had a cannon in his thigh-leg bones. A bit larger than a finger...
--Paul E Musselman