As of now, several countries operate Boeing 737 aircraft for military purposes, utilizing various models of the aircraft for different roles such as transport, surveillance, and training. Here are some notable examples:

1. United States: The U.S. military operates the Boeing 737 in several variants, including the C-40 Clipper, which is used for transporting personnel and cargo.

2. Turkey: The Turkish Air Force operates the Boeing 737 AEW&C (Airborne Early Warning and Control) variant, known as the Peace Eagle, for surveillance and reconnaissance missions.

3. Australia: The Royal Australian Air Force uses the Boeing 737 in the form of the P-8 Poseidon, which is primarily used for maritime patrol and anti-submarine warfare.

4. Brazil: The Brazilian Air Force operates the Boeing 737 in a VIP transport role, as well as for other logistical purposes.

5. Mexico: The Mexican Air Force has utilized Boeing 737 aircraft for various military transport roles.

6. Indonesia: The Indonesian Air Force operates Boeing 737 aircraft for transport and logistical support.

7. Pakistan: The Pakistan Air Force has also used Boeing 737 aircraft for transport and other military operations.

These countries leverage the versatility of the Boeing 737 platform to fulfill various military needs, from transport to surveillance. The specific models and configurations can vary significantly based on the operational requirements of each country.