Which of the following actions is necessary to load the M203 grenade launcher?

To successfully load the M203 grenade launcher, unlocking the barrel latch is a critical step. This action allows the operator to access the weapon's chamber, enabling the insertion of the grenade round into the launcher. Properly unlocking the barrel is essential as it facilitates the continued operation of the weapon, ensuring that the round can be loaded securely before proceeding to typical firing procedures.

Pressing the safety switch is a safety measure but does not pertain directly to the loading process. Pulling the trigger is related to firing the weapon, while checking scope alignment is necessary for aiming but not for loading. When preparing to use the M203, following the correct loading procedure, including unlocking the barrel latch, is vital for safe operation and efficient use of the weapon.