Descent upon and First strike

First strike and descent upon are semantically related In some cases you can replace phrase "First strike" with "Descent upon", this phrases are similar.

First strike noun - The initial use of nuclear weapons to attack a country that also has nuclear weapons; considered feasible only when the attacker can destroy the other country's ability to retaliate.

Descent upon and first strike are semantically related in tactic in warfare topic. You can use "Descent upon" instead a noun phrase "First strike".