This is a fairly fascinating tale of military leapfrogging:
Sweden Has A Sub That’s So Deadly The US Navy Hired It To Play Bad Guy: “We have been glued all week to the sub saga off the coast of Sweden, where six days in Swedish forces have only now called off their search for an elusive sub hiding in the waters off Stockholm. Yet what nobody has mentioned is just how deadly and capable Sweden’s own subs are, and there are few better weapons for catching a sub than another sub.”
I would totally have worked that into Arctic Rising if I’d known.
Something to come back to in the third novel, possibly.