The plasma sidearm issued to Enterprise NX-01's crew at launch in 2151, awkward to aim and soon replaced by the new phase pistol with its stun and kill settings.
The EM-33 is the hand weapon carried by the crew of Enterprise NX-01 at the very start of its mission, seen in the pilot episode Broken Bow. It fires bolts of plasma rather than a continuous beam and has no stun setting.
Archer and his officers use EM-33s during the firefight with the Suliban on the roof of the trade complex on Rigel X, where Archer is shot in the leg.
Before the raid on the Suliban Helix, Malcolm Reed unpacks a case of the newly delivered phase pistols and explains their two settings. From then on the phase pistol is the ship's standard sidearm.