The power of the Ottoman Empire was largely based on war and conquest. The military was its most important institution. The Istanbul Military Museum puts that on display. The museum originally opened in 1950 and housed in an old church. In 1993, it moved to its current location in the old Ottoman imperial military academy.
As one would expect from a military museum, it is filled with the tools of war. There are more than 9,000 artifacts from the Ottoman period up through World War II. Exhibits on display include chain mail, bronze armor, swords, rifles, and tents. Some highlights include the enormous chain that the Byzantines draped across the Golden Horn to [unsuccessfully] keep out the Sultan's navy. The Mehter Takimi is the world's oldest military band, as the Ottomans were the first to use music in the military. A performance is held every afternoon.
The Istanbul Military Museum is a can't miss for anyone interested in military history. Lots of fascinating objects are on display here. The daily Mehter Takimi concert is surprisingly moving. The displays aren't as well marked as in many western museums, so you may find some exhibits lacking in context. Still, this is a great attraction.
Location: Cumhuriyet Cadde, Harbiye
Hours: Open Wednesday through Sunday 09:00-17:00.