Sounds like the Oregon Iron Works (OIW) Sea Scout Unmanned Tactical Seaplane. If so, it wasn't ONR but a NAVAIR Small Business Innovative Research incentive (although Wikipedia says that Sea Scout was funded by DARPA as part of a 2005 Vought study).
OIW Sea Scout had a 38hp Wankel rotary engine, weighed 300 lbs, and carried a 25 pound payload. The airframe was based on the wheeled Daedalus/Geneva Aerospace Dakota UAV.
http://www.designation-systems.net/dusrm/app4/dakota.html
It seems there were variations on the theme. As launched in 2006, the Sea Scout had 10 ft wings with endplate tip floats. Later it sprouted 17 ft wings with outboard dihedral and more conventional tip floats on struts at mid span.
http://www.flightglobal.com/assets/getAsset.aspx?ItemID=13002
http://www.oregoniron.com/wp-content/gallery/marine/unmanned-air-vehicle-uav-sea-plane.jpg