1.
military strength; fighting power
The combat capability or armed forces of a nation or military unit.
戦力を増強する。
To strengthen military power.
憲法は戦力の保持を禁じている。
The constitution prohibits the possession of military forces.
両国の戦力には大きな差があった。
There was a large gap in military strength between the two countries.
2.
key player; valuable asset; contributor
A person who is a major contributor to a team, company, or project. Figurative extension of the military sense, commonly used in sports and business.
彼はチームの即戦力だ。
He's an immediate asset to the team.
新人が戦力になるまで時間がかかる。
It takes time for new hires to become productive contributors.
エースが怪我で離脱し、大きな戦力ダウンとなった。
The ace left due to injury, resulting in a major loss of strength for the team.
In the context of Japan's constitution, Article 9 famously states that Japan renounces 戦力の保持 (the maintenance of war potential). In everyday use, the figurative sense (sense 2) is very common, especially in sports and business. Key compounds: 即戦力 (someone who can contribute immediately), 戦力外 (not a contributor; dropped from the team roster).