Retired Navy Capt. Philip Van Horn Weems, a veteran of both World Wars, inventor, and instructor of astronauts, died of pneumonia Saturday at Anne Arundel General Hospital in Annapolis. He was 90.

Capt. Weems was the developer of the Weems Systems of Navigation, the second-setting watch, the air almanac, and star curve charts.

At the age 72, he was ordered to return to active duty by the Navy to help develop a system of space navigation. With the help of what was described as "four near-genius" ensigns, he invented a quick way for astronauts to determine their position relative to the earth by a few visual sightings. The system did not need computers.

In 1962, he taught navigation classes at the U.S. Naval Academy at Annapolis and tutored some astronauts in advanced navigation techniques.

He also was a consultant for NASA as a space navigation specialist.

Following his third retirement from the Navy, in the 1960s, he kept busy skin-diving, hunting sunken treasure in the West Indies, and working on inventions in his Annapolis home.

Chief Justice of the United States Earl Warren presented Capt. Weems with the gold John Oliver La Gorce Medal of the National Geographic Society in a 1968 ceremony.

Capt. Weems was a 1912 graduate of the U.S. Naval Academy and a classmate of Adm. Richard Byrd. Capt. Weems was an all-American center on the Navy football team, and was on the U.S. Olympic wrestling team at Helsinki in 1920.

The future tutor to astronauts taught navigation Charles Lindbergh and Wiley Post. Capt. Weems also handled the spinaker on the last cruise of the Navy's square-rigged sailing ship Hartford.

"My generation is the last one that still kept in contact with basics, with principles. Now we spend billions and billions on black boxes - radar and computers and all - but too many people are ignorant of the principles that these things are all about," Capt. Weems said in a 1968 interview in The Post.

He was born on a farm in central Tennessee. He was an eighth cousin of Parson Weems and Dr. Harold Edgerton, perfector of the strobe-scope for high-speed photography. Capt. Weems' father had been a scout for Confederate Gen. Nathan Bedford Forrest.

Capt. Weems was orphaned at the age of 12, but not separated. They managed the family farm themselves. Capt. Weems attended a one-room school house before going to Annapolis.

He saw duty both here and abroad before retiring from the Navy the first time in the 1930s. He was recalled to active duty in World War II and served as a convoy commodore in the Atlantic.

He retired a second time following the war.

His elder son, Marine Corps Maj. Philip Van Horn Jr., was killed in combat in the Southwest Pacific in World War II. His younger son, Navy Lt. Cdr. George Thackray, a former Olympic wrestler, was a Navy test pilot. He was killed in a 1951 crash of his plane.

Survivors include his wife of 65 years, Margaret Thackray Weems, of the home; a daughter, Margaret Dodds, of Annapolis; three grandchildren, and three great-grandchildren. CAPTION: Picture, Retired Capt. P. V. H. Weems holds plastic spheres that allow astronauts to determine their location. AP