I went by one Sunday and was given the tour by one of the members. It is a really cool museum. Luckily, the guides are really good at hitting the highlights, or you could get lost in there for hours. There are lots of really cool military artifacts. The members are working diligently to label and research many of the items thats history has been lost to time.

Our friends at Wikipedia had the following to say:

The company's stone and brick armory building, located at 23 Clarke Street in Newport, was constructed in 1835 in the Greek Revival style. The work was overseen by master stonemason Alexander McGregor.

The armory houses a museum that features an extensive collection of military uniforms from over 50 different nations. The museum also features the uniforms of prominent individuals such as Medal of Honor recipient General David M. Shoup, General Colin Powell, General Creighton Abrams, General William Westmoreland, Fleet Admiral Chester W. Nimitz, Admiral Cameron Winslow, Colonel Katherine Amelia Towle, President Anwar Sadat of Egypt, Admiral of the Fleet Earl Mountbatten of Burma, Field Marshal Viscount Montgomery of Alamein, HM King Hussein of Jordan, HRH Prince Philip, Duke of Edinburgh and HRH Prince Henry, Duke of Gloucester.

The museum also contains several artillery pieces, including four bronze cannons cast for the state of Rhode Island by Paul Revere in 1798.

The Newport Artillery's armory was listed on the National Register of Historic Places in 1972.