That is a beautiful area and I’m ashamed to admit I’ve never taken the time to visit it on foot.
The Navy Memorial is on the north side of PA Ave. about have way between the White House and the Capitol.
http://www.navymemorial.org/about.php
The Navy Memorial that you mentioned, along PA Ave at 7th Street, was built in the 1980s. The other memorial, which I referenced before, is the Navy & Marine Memorial. It lies in Lady Bird Johnson Park, across the River, along the GW Parkway just before the 14th St. Bridge. Here’s a nice description of it, along with some info on another beautiful memorial, for the Titanic:
http://adams.patriot.net/~eastlnd2/rj/pl/dc/gulls.htm
Another lost Titanic memorial is the Butt-Millet fountain in President’s Park, in the Ellipse, jsut below the White House. It was dedicated to Maj. Butt and his friend, Francis Millet, who went down on the Titanic. Butt was ADC to President Taft, thus the prominent placement of the memorial at the foot of the White House.
http://www.dcmemorials.com/index_indiv0000860.htm