Possible Clues:

• Works on firing kit manager of Arsenal?
• A Royal Mail server, powerless as a mail keeper
• Custodian of pieces etc?
• Prepares Arsenal, as those doing the shooting are relying on him
• Mail worker set our letters on postbox
• King enters affair with army corps backing — he has weapons
• Provider of weaponry in a group of jolly types accompanying our monarch
• Maker of weapons or mail
• He'll deal with the mail