I. America Observes British Air Rescue Operations
During the Battle of Britain, Nazi Germany was beginning their first phase in the conquest of the United Kingdom.  Namely, prior to landing troops on British beaches, the German Air Command was ordered to liquadate all British Air Forces who would otherwise destroy or severely cripple German invasion forces.
To paraphrase then UK Prime Minister Churchill, " never has so much been owed by so many by so few..."  In short, a thin Royal Air Corps line was drawn between those invasion forces and the jugernaut of the combined German armed forces.  These were the British fliers.  The airmen and the air crews.
With an almost three to one advantage, the Luftwaffe (German Air Forces) launched a devistating attack on the British Isles in advance of their Operation Sea Lion.  Despite German numerical air superiority (and of course the vanity of thinking they were a superior race anyways), the British Air Corps held their own and eventually turned the tide on this air war over British skies.
II.  Saving Pilots to Fight Another Day
Since there were far fewer qualifed combat pilots than there were combat plans, it became imperative to try and save the lives of as many shot down fliers as possible so they could "fight another day!"
Hence, the need for a rescue craft specifically designed to pick-up downed airmen.
III.  America Adopts a Crash Boat Program too
Based on the experiences of the British rescue boat program for their air crews, America began to plan for a rescue fleet well in advance of the Japanese attack on Pearl Harbor.  Most in the military (and civilian leadership) knew it was simply a matter of time before our Atlantic and Pacific motes would no longer protect us from international events.  Once Japan and Germany conquered their immediate objectives, well, we were "next."   Isolationism was not going to work.  And so the work began on this one aspect of a global war.
The word Crash Boat refers to an armed rescue boat deployed to save air crews who had to crash (or ditch) their plane.  Later, this term could be applied to any surface vessel that was disabled, sinking or needed assistance. 
Our nation developed five specific types of "Crash Boats" based on range and speed.  The largest Crash Boats were called the "104s"   meaning they were one-hundred and four-feet long.  The 104s had the greatest range but were, relative to other enemy small boats, slow.
The next Crash Boat was known as the "ASR 85s" standing for Air Sea Rescue and the length of the boat which was eighty-five feet.  The ASR 85s enjoyed range and speed and therfore considered by many to be the most effective Crash Boat design.
For near coastal and an intermediate offshore range there was the AVR63.  The Air Vehicle Rescue vessel was sixty-three feet long and possessed great speed with intermediate range.
The last two vessels were limited to near shore and inland waterways.  They were recreational boat designs drafted for war time use of the forty-five and twenty-five feet variety.
IV.  Specific type history - first the AVR 63s - a brief outline
AVRs (Air Vehicle Rescue) are very special vessels.  They were designed by the US Navy during World War II.  AVRs, compared to the more well-known PT boats, were relatively lightly armed (four fifty calibur maching guns - two per station -  with two Mk6 depth charges on the aft deck).  Their role was to swoop-in fast and retrive downed airmen in the Pacific, Atlantic and Mediterranean waters - so they could fight another day.  Their primary defense system was speed and manuverabilty.  In short, they were armed rescue boats.
However, some AVRs were assigned the role as a subchaser and patrol boat.  In this role, AVRs beefed up their offensive systems to include three to four depth charge racks aft with an extra sixteen charges stowed in the aft deck.  In addition, a 20mm Oelikon machine gun was mounted on the aft deck.  Moreover, many crews in the South Pacific theater mounted an additional 50 caliber on the bow.  The latter gun bow provided addtional firepower and more weight on the foredeck to assist the vessel in getting on a plane sooner and hence achieve a faster "flank speed" mode.  They were also built very strong thus the longevity of so many of these beloved "little ships" of the US Navy.   They are also referred to as Crash Boats - meaning when a plane or other object "crashes," the role of the AVRs was to retrive survivors.
AVRs would serve in World War II, Korea, during the Cold War and the near coastal waters of the United States.  They would also serve in many of our Allied nations fleets (example, the Australian Navy).  With respect to the US Navy, the last AVRs were decommissioned in the very late 1960s and early 1970s.  A massive decommissiong of these vessels took place following World War II.  AVRs ended up in private hands and were also widely used by Sea Scouts from the San Francisco Bay beginning in the late 1940s.  A few other AVRs were used by Sea Scouts on the East Coast and the Pacific Northwest.
V.  The Other Crash Boats
There's a lot more interesting tales to share about the contributions of the 104s, ASR 85s and the 45s and 25s.  We here at the Maritime Learning Center will be posting additional histories once our research teams complete their initial reviews.  Stay tuned for more exciting history about the people who made the boats, sailed them, and the air crews they saved! 
American Crash Boat Builders, circa 1942