A "P" boat under the U.S. Army designation system was a Patrol or rescue vessel. When the USAF inherited the Army boats, they completely changed the numbering sytem but started the number with an "R". The Navy used a "C" for theirs while the Coast Guard used "CG". Other prefixes you will see in Army O(ther) include "Q" for personnel vessels of roughly cabin cruiser size and "QS" for fast supply boats. The final prefix found here is "J", used to designate launches of many types and sizes.
There are more boat numbers listed than there were boats produced. The reason for this is that some boats originally produced for the Navy were transferred to the Army. If I have no information linking a specific Navy hull number (ex: C-***) to a specific Army number (P-***) that hull will probably listed twice. If on the other hand I did have information linking a specific Navy Hull number to a specific Army hull number, then the hull will be listed once, with both numbers appearing on the same line.
Emergency Rescue Boat Squadrons
1st ERBS Mediterranean
2nd ERS No boats, OA-10A Catalinas assigned to the 5th Air Force in 7/44
3rd ERS No boats, 12 OA-10A Catalinas assigned to the 5th Air Force
4th ERS No boats, OA-10A Catalinas assigned to the 20th Air Force
5th ERBS European theater, then sent to the Pacific 7/45
6th ERBS Assigned to the 5th Air Force in the Pacific, Okinawa
7th ERBS Transferred from India to Okinawa 8/45
8th ERBS Based in the Mediterranean., apparently overlapping the 1st ERBS
9th ERBS Unknown
10th ERBS Alaska and all the Aleutian Islands, to the Kurile Islands
11th ERBS Eastern Caribbean.
12th ERBS Western Caribbean, covering all of Panama and surrounding waters of the Pacific, and part of S. America.
13th ERBS Hawaii (previously the 927th Quartermaster Boat Company (AVN)
14th ERBS Assigned to the 5th Air Force, along with the 2nd ERBS in the Pacific
15th ERBS Assigned to the 13th Air Force in the Pacific.
6th CRBS Bermuda during the 1950s.
22nd CRBS Korea, Japan, and the Pacific during the Korean War.
Much, but not all, of the data comes from "Report of Army Small Boat Construction, 1 July 1940 to 31 May 1945" and " U.S.. Army Ships and Watercraft of World War II". Another extensively used source was "Crash Boats" by Dave Linley & Terry Holham. Additional data came from George Schneider, who has extensive records of the boats. Two 94 ft. prototype boats were built in 1955 or 56, but the program was dropped. The 83-foot boats were Design 203, built at the beginning of the air sea rescue boat program.
* 72' boats pre-WWII boats, 15' beam. One each was Located at MacDill (FL), Bolling Field (DC), and Bermuda.
** 83' boats, design #203, with 32 built, are probably a USCG design. Some USCG #s overlap rescue boat numbers. Some sources show them as 84' Boats.