1. Apology. I only saw these messages as of July 2008, and I hope you get to see this reply.
2. I have been researching the service of my father and uncle in WWII. Dad served in H&HQ Battery, 762nd AAA Gun Battalion. Uncle in Battery A, 766th AAA Gun Battalion. As a result, I have been researching this service since 2000. I expect to publish this research in book form. I also belong to a group that interprets the Coast Artillery at several old posts. This is the American Ground forces Association. I wear the uniform and insignia of soldiers of the 21st Coast Artillery (Fort Mott, 1940) and the 245th CA (Fort Hancock, 1942-43).
3. Please see replies to Ol Uncle Bob and to Digger. In 1936, antiaircraft artillery was under Coast Artillery, and organized as regiments. Each regiment had two battalions and one battery, among other service units. 1st Battalion was a gun battalion of 3-inch guns. 2nd Battalion was a machine gun battalion. There was a searchlight/sound locator battery. In 1942, this battery was to be expanded to become 3rd Battalion. If there was a need to have two or more regiments together, these regiments were assigned to a brigade.
4. In Dec 42, it was proposed and accepted the AA regiments be broken up. So it was that battalion designated as 1st became the AAA Gun Battalions with 3-inch, 90mm, or 120mm guns. Battalions designated as 2nd Battalion became the AAA Auto Weapon Battalions. 3rd Battalion became AAA Searchlight Battalions. As a general rule, in official papers, anytime a unit had "CA (AA)" in its designation, it was a reference to the regiment. If it had "AAA" it was to the new structure of a battalion. 60th Coast artillery (AA) was a regiment in the Philippines. 762nd AAA Gun Battalion was a new structure battalion.
5. The new battalions had to report to a headquarters. Groups replaced the old regimental designation. These groups would use generally speaking the old regimental number. The group was under a brigade. however, territories did have a different structure above regiments.
6. My guess is that the 4th CA you mention was the 4th CA Group, in charge of the 765th AAA Gun Battalion. Do not recall if the 765th AAA was to be replaced by drafted Puerto Ricans as I do not have my notes. For an explanation of this, read my reply to Digger.