Until an investigation is completed, one can only speculate on the cause of the explosion that killed 47 crewmen in a massive gun turret aboard the battleship Iowa.

At this point, about all that's certain is the magnitude of the tragedy - the worst naval disaster in more than a decade and one of the worst since World War II.What also should be reasonably clear is that the investigation needs to go beyond finding out precisely what went wrong in this particular accident. Let's also determine if enough modernization was done when the 47-year-old Iowa was taken out of mothballs and reactivated five years ago.

We raise this point because a current account describes the six-story gun turret that exploded aboard the USS Iowa on Wednesday as "a dark and oily antique crammed with silk bags and gunpowder and mammoth steel shells - where a single hot ember or wayward spark could cause disaster."

Moreover, though both the turret and the ship were made of thick steel and designed to keep a fire or explosion in one compartment from spreading, is there no way to keep such precautions from turning the turret into what military experts call a "steel tomb" for sailors if something goes wrong? The turrets are said to provide no escape for anyone from fire, heat, blast and debris.

Though this week's disaster during exercises in the Atlantic is reviving debate over the wisdom of the decision to reactivate the Iowa, that step still looks sound.

The Iowa was one of four battleships (the others are the Missouri, the New Jersey, and the Wisconsin) pressed back into service in the early 1980's as an effective way of displaying and exercising America's might. The Iowa, for example, returned home last year after having escorted Kuwaiti oil tankers in the Persian Gulf. The Iowa's 16-inch guns, capable of firing shells weighing more than a ton a distance of 23 miles, are still the largest in use by any Navy. In fact, the skills for building such mammoth guns no longer exist. The ships themselves are dwarfed only a couple of Japanese battlewagons, also of World War II vintage. Moreover, reactivating a mothballed battleship cost the United States less than it took to build a brand-new guided missile frigate. Besides its big guns, the Iowa and its sister ships carry Tomahawk and Harpoon missiles.

Keep in mind, too, that extensive precautions are taken to avoid accidents and that disasters like the one this week aboard the Iowa are extremely rare. The last previous turret explosion on a battleship occurred in 1943 aboard the USS Mississippi, killing 43. A similar accident occurred with a smaller turret on the cruiser Newport News in 1972 off the coast of Vietnam, killing 20.

Meanwhile, as America mourns the 47 dead crewmen and sympathizes with their families, an expression of deep gratitude is also in order not just to the crew of the Iowa but to all those who risk their lives to keep America strong.