The Navy Museum, in building 76 at the Washington Navy Yard, 9th and M streets SW, is open from 9 a.m. to 4 p.m. Monday through Friday and 10 a.m. to 5 p.m. Saturday and Sunday.

If this is Thursday, then it must be "sky day." Wednesday was "ship day" and Tuesday, "sea day."

Confusing? Perhaps, if you're anyone other than John C. Roach, an Alexandria artist who is in the throes of completing what must be one of the largest ship paintings in Navy history.

His 16- by 52-foot mural of the battleship Arizona, now taking final form at the Navy Museum in Washington, is so large it has given Roach headaches few artists encounter.

Take maintaining perspective. To do that, Roach alternates the sections he paints, spending one day on the sky, the next on the ship and then the sea.

The painting is so big -- "I didn't know how big it would be when I dipped my oar in" -- that he concedes, "I have difficulty seeing the whole thing."

To get a better view, Roach, a lean 6-footer best known for the painting of Navy ships that line the Pentagon's executive corridor, often scrambles into the rafters of the museum, a former gun factory.

When completed, the paiting will hang in a new memorial now under construction by the Navy at Pearl Harbor, where the Arizona was sunk on Dec. 7, 1941, in the attack that brought America into World War II. But that's 6,000 miles from Roach's tiny Northern Virginia studio, where he does most of his painting.

The studio, behind Roach's home at 804 Albany Ave., is so small that he had to ask the Navy to help him find a place large enough for the Arizona canvas. The service suggested the museum in the Navy Yard, where Roach's work has become a main attraction.

"Everybody who's been through has just been fascinated by it, especially the size," says Cmdr. Tad Damon, the museum director.

Even thought he painting is immense, it is only one-twelth the size of the 600-foot Arizona. Getting the paiting to Hawaii when Roach is finished, probably in late August, will require shipment on a military cargo plane, which the Navy will arrange.

The painting was commissioned by the Pearl Harbor Survivors Association, a group of servicemen who lived through the Japanese surprise attack, which demolished much of the Navy's Pacific Fleet and killed 2,341 persons.

The survivors association will donate the painting to the Navy for the $4.2 million memorial at Pearl Harbor. The Navy expects to complete the memorial late this summer or early fall and turn it over to the National Park Service.

For Roach, 37, a native of Newport News, the Arizona painting is the latest in a series of works that has brought him much acclaim from the Navy. Many of the nearly 150 ship paintings were done when Roach was a journalist covering the Pacific Fleet during the Vietnam conflict.

More recently, as a lieutenant in the Navy Reserve, Roach was given the Navy Achievement Medal for his works. Many of those works have been reproduced by the Navy and are found in U.S. military offices and ships around the world.

For the Arizona, Roach did a considerable amount of research, including numerous pen-and-ink sketches and a trip to Hawaii, before he was ready to begin work on the canvas.

"What I wanted to do was to depict the Arizona as it appeared in its peacetime configuration, when it went out to Hawaii, about six months before it was sunk," Roach says. "In its final six months, the ship underwent numerous changes because it was being readied for possible combat in the Pacific."

Roach says he chose the configuration because that was the way the Arizona looked for the longest period of time and is best remembered by her crew. He also has depicted the destroyer escort Downes, one of 18 ships sunk at Pearl Harbor, in the painting.

The Arizona is the final resting place of 1,102 crewmen who went down with the battleship during the Pearl Harbor attack.

Roach's father, Charles D. Roach of Newport News, was a naval architect, and ever since the younger Roach can remember peering over his father's drawing table, he has wanted to draw ships, design them, or at least go to sea in them.

"If you're in Newport News, you can't help but be aware of the Navy and ships," he says.

In addition to the Arizona project, Roach is working on a painting of the guided missile frigate Arkansas, now under construction in Newport News. that painting will be "smaller 30 by 40 inches," Roach says. "Of course from now on, all of my paintings are going to be smaller."