The Air Force did issue them to pilots at one point, although I don't know if they're still in use, or if they were replaced with the FN 5.7 as announced.
FBI and US Marshals issue Glock 22.
No
Probably never.
A Glock 45 is a semi-automatic pistol. Glock pistols are a very popular type of pistol. In particular many law enforcement agencies in the US use them.
Originally made i Austria, there is now a manufacturing facility in Georgia (the US State of Georgia)
The companies, or the firearms? Glock USA is an importer. Since Glock pistols cannot be shipped as is due to the provisions of the Gun Control Act of 1968, they have to be shipped with adjustable sights in order to be importable. Glock USA receives the pistols, removes the adjustable sights, and replaces them with the standard fixed Glock sight, manufactured in the US. The firearms themselves are pretty much the same, except American Glocks are sold with American made sights. The only other difference is that the .380 ACP Glocks - the Glock 25 and Glock 28 - are not available in the US as they cannot be made to meet the criteria of the Gun Control Act of 1968.
Mainly because the glock has no external safety which is a requirement for the U.S Army.
Glock 22 .40 cal handguns
The Gun Control Act of 1968 set forth certain criteria which firearms manufacturers must meet before their firearms can be imported for resale on the US civil market. Even the Glock pistols which are sold in the US must be shipped with adjustable sights, which are then replaced with fixed, US manufactured sights once they arrive. The Glock 25 does not meet the criteria sufficiently to be allowed for import onto the US market.
Austria and the US, although all are stamped AUSTRIA. They're stamped Austria because they're all made in Austria. The "US" pistols have to be shipped with flimsy adjustable sights in order to be legally imported into the US.. all the US division of Glock does is replace these with US-made fixed sights.
NoAdded: I believe that it was among many types and other manufacturers that were tested by the military, but the US military ultimately chose the Beretta 9 mm as the chosen service pistol.Interestingly enough, certain "special ops" groups are authorized to be armed with pistols (and other firearms) of THEIR choice without regard to the Beretta.
If I were to take a guess as to why you have one in the Philippines with US markings.... If it's a service issue weapon, probably because it was delivered through a US military/law enforcement aid programme. When such funds are distributed from the US government, it's usually with a stipulation that it be used to buy materiel from US companies, and, in order to purchase Glock pistols with these funds, it would be required for them to go through the US subsidiary, rather than direct through the Austrian one. Looking at a brief rundown of gun laws there, it seems to give the impression that individuals authorised to own such firearms have the ability to have them imported, as well, although I could be misreading it.