In navyfield 1 all ships had three different types of High Explosive shells: LHE, SHE & HHE (light, standard and heavy)

The differences between the shells is their range, damage & capacity on board. Lighter shells have more range and deal less damage. Heavy shells do more damage but have shorter range.

Equipping lighter shells meant you could have slightly more in total. Say if you had 160 standard shells, you could have 176 Light shells, while only 148 Heavy HE shells. (as a rough example)

This allows players to drive a ship to suit their playstyle. If you want to do more damage you can. If you want longer range, there you go.