B737-800
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Confusion; Troubleshooting
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Returned To Departure Airport; Flight Crew Requested ATC Assistance / Clarification; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Operating ZZZ to ZZZ1 ; aircraft came in with multiple MEL. Biggest threat we saw was deferred pack 2; and pack one controller fail on pack 1. Legal time Dispatch; weather was great; filled at 240; had to stay below 250 per MEL. Departed ZZZ; got to cruise; accomplished cruise check. Pack 1 then failed in flight; hit the master caution  to clear; pack still failed. Don 02 masks; requested 10;000 ft.;requested priority handling; I executed a rapid descent; Captain ran the depressurization check list and deployed passenger oxygen masks. By the time we got to 12;000 ft. or so we got the cabin altitude high warning. Got to 10;000 ft. alarm going off still. Descended to 8;000 ft.; did a 180 turn back to ZZZ. Took off O2 mask and landed overweight in ZZZ.I think the training department did a great job in training us for a random event like this; as well as the threat forward thinking; dispatched with one pack; it was in our departure brief etc. Overall it was a nerve racking event; but when that Master Caution showed up on the panel; we went into respective roles and got the aircraft down and gave the passengers oxygen and returned to the field. The passengers were pretty happy with us after going through that; we're clapping as we landed in ZZZ. Overall; training did a great job preparing us for something like this I think.
B737 First Officer reported the aircraft failed to pressurize after takeoff and flight crew elected to make a rapid descent and air turn back; resulting in a safe precautionary landing.