Read this: Armies typically have air defence in depth, from integral MANPADS such as the RBS 70, Stinger and Igla at smaller force levels up to army-level missile defence systems such as Angara and Patriot. Often, the high-altitude long-range missile systems force aircraft to fly at low level, where anti-aircraft guns can bring them down. As well as the small and large systems, for effective air defence there must be intermediate systems. These may be deployed at regiment-level and consist of platoons of self-propelled anti-aircraft platforms, whether they are self-propelled anti-aircraft guns (SPAAGs), integrated air-defence systems like Tunguska or all-in-one surface-to-air missile platforms like Roland or SA-8 Gecko.

What does SPAAG stand for?
What is the answer? (If it cannot be answered, return "unanswerable")
self-propelled anti-aircraft guns