Non-native speaker here. What's an "HE shell"? The article doesn't seem to define it, and to my surprise, even the Wikipedia page on shells (projectiles) [1] s

Non-native speaker here. What's an "HE shell"? The article doesn't seem to define it, and to my surprise, even the Wikipedia page on shells (projectiles) [1] simply uses the terms "AP shell" and "HE shell" without bothering to define (or link to) either. After 15 minutes of fruitless research, I gave up. What am I missing? [1]: https://en.wikipedia.org/wiki/Shell_(projectile) https://en.wikipedia.org/wiki/Shell_(projectile)