A "CASREP" was a "casualty report." CASREPs were not sent out for people being hurt, but for equipment damage/failure. There were two categories: Combat systems readiness (C) and engineering (mobility) (M) readiness.
C1 and M1 meant that the ship could sail and fight. A 2 level meant that there were minor, but serious degradations. A 3 level meant that there were damn serious degradations. A 4 level meant, in common parlance, that the ship was broke-dick and wasn't going anywhere.
Actually, it wasn't that clear-cut. While a M4 CASREP meant "we ain't getting underway, or if at sea, "send the tugs", a ship might possibly sail with a C4 CASREP. The combat systems CASREPS were by warfare area, so for ASW, the ship might be completely dead, but it could still shoot its guns or fire missiles. If part of the mission was armed diplomacy ("showing the Flag"), then it didn't matter if the Tartar launcher was broken.
CASREPs were sent by teletype radio message. The effect could be like kicking over an anthill, often as the shore establishment scurried around to fix the things that they should have fixed anyway. A simple lack of repair parts could trigger a CASREP, which was really embarrassing to the supply pukes if that part was supposed to be in ship's stock.
CASREPs could also request technical support. This was common in serious leaks in the main steam piping, as repairs required highly certified welders and X-ray quality control examination of the welds. Usually the staff pukes confined their assistance to expediting parts and technicians and refrained from offering their idea of helpful (and unsolicited) advice, but not always.
If a part was needed and not available, the supply system would sometimes send the "next higher assembly". I once saw an entire antenna assembly delivered for a SPS-49 because the radar repair guys needed one part from it.
The more twisted mess was when the supply system's records indicated that there was no part available. Sometimes the divisional supply petty officer would go over to the supply center and do a physical stock check. That could be embarrassing for the supply pukes if they really did have the parts.
This is no shit: There once was a minesweeper in drydock that needed a new dunce cap. The supply system said that there was not one available and that one would have to be manufactured. So one day, one of the more worthless division officers went to check out with the XO and go home (this was around 1300). The XO felt like screwing with that junior officer, so he told him that he could leave after he drove over to the supply center and got a new dunce cap.
This kid was dumb enough that he had no clue what the proper procedure was to go get parts from the supply center. What he did do was to drive his car to the base supply center and drive around until he saw where those parts were kept. He asked the grizzled chief there if they had any dunce caps for that class of MSO. The chief said: "Yeah, I got them, how many you want, sir?" The kid signed where the chief told him to sign, the chief had a couple of guys put the dunce cap in the kid's car (they weren't that big) and the kid was soon back at the ship, showing the dunce cap to the stunned XO.
The supply system was also good at losing parts. I knew of one double-ended cruiser which had one of the motors in its aft launcher burn out. They CASREP'd the launcher and a new motor was sent. It disappeared en route. The supply system said that it had been delivered, the ship denied receiving it. Now this was no tiny motor, it was a big-ass 440 volt motor with a fair amount of horsepower. A second motor was sent and installed. Six months later, the first motor mysteriously appeared on the pier alongside the ship. There was no tracking paperwork, nobody knew who delivered it or where it came from. It was just there.
CASREPs could be (and often were) amended. A CASREP level might be reduced if the ship's force was able to jury-rig a partial repair. When the casualty was fixed, a CASCAN (casualty cancellation) was sent out.
 I believe that the CO of an AO or AOR did once send out a CASREP for undermanning.
 And maybe the Soviets didn't know that the best ASW ship in WestPac had all of the ASW capability of the Staten Island Ferry.
 My recollection is that the USS Compte de Grasse was sent on a "show the Flag" cruise to France soon after she was commissioned, interrupting the ship's training at Gitmo.
 The techs just cannibalized the part from the antenna on the pier, took the broken part off the installed antenna, installed the new part and it worked. they then put the bad part into the antenna on the pier, marked the thing as "unserviceable" and sent it back. The supply pukes ashore were not amused and complained. The ship had, by then, cleared the CASREP and nobody gave a damn.
 Fill out a Form 1250, have the XO sign it, take it to the ship's supply department, where they would then type out a Form 1348 and take that to the Supply Center. Doing this when the ship was in-port could alleviate the need for a CASREP. If they would give you the part. Sometimes they wouldn't.