A powerful ship-mounted weapon sold to Voyager by the Entharan arms dealer Kovin in 2374, a purchase overshadowed by Seven of Nine's accusation that he had assaulted her.
The isokinetic cannon is a weapon offered for sale by Kovin, an Entharan trader, in the Voyager episode Retrospect. In a demonstration it punches cleanly through a heavily armoured target, and Captain Janeway agrees to trade for it to strengthen her ship's defences.
While Kovin is aboard to help install the cannon, Seven of Nine strikes him. Under the Doctor's guidance she recovers what seem to be suppressed memories of Kovin taking Borg nanoprobes from her by force.
The evidence turns out not to support her account, but Kovin, fearing ruin under strict Entharan law, flees and fires on Voyager. His overloaded ship explodes, leaving the Doctor and Seven to face what their certainty has cost.