ALO FAC F19 patch -- This one is unknown to me, so if you have information about it, please share. I believe ALO is an acronym for Air Liason Officer (but could also be Aircraft Light Observation). So maybe this was a SVN Officer patch that acted as a Liason to the Army FAC units. I don't know...I'm just guessing. I'm unsure what the F-19 represents but it is also used on the companion patch (small diamond patch). The moto under neath the plane "Mot Minh Khong So" translates to "Alone and Not Afraid", which fits a FAC pilot's mission, flying alone in a single engine prop plane high above the jungles of Vietnam.
I believe I have an explanation for the "F-19" designation that you see on this patch.
The 0-1 Bird Dog observation planes were originally designated L-19 when the planes were first purchased by the US Army for the Korean War. According to an entry on Wikipedia "The Defense Department ordered 3,200 L-19s that were built between 1950 and 1959. The planes were used in various utility roles such as artillery spotting, front-line communications, medevac and training. In 1962 the army L-19 was redesignated the O-1 (Observation) Bird Dog and entered its second war in Vietnam."
The website that DaveP provided gives a further explanation with the history of the 505th Tactical Control Group:
"By April 1963, 32 PCS Liaison Officers in Vietnam were assigned to each Corps and Division with regiments covered on an "as needed" basis. The VNAF provided L-19 FAC vehicles at division level until the arrival of the 19th TASS with 22 O-1Fs in July 1963."
The ALO were USAF pilots serving as Air Liason Officers. This unit provided the beginnings of Tactical Air Control during the early stages of US involvement in the War.
Now for the "F-19" designation.... Many of these pilots were fighter jocks. They weren't quite thrilled to be considered anything less than a fighter pilot, so they unoffically renamed their aircraft with the "F-19" designation! This is further borne out by the "Mach .2" speed rating, as opposed to "Mach 2"!
This has always been one of my favorite patches, both for the history and dry sense of humor.