Truth in labeling has achieved a rare breakthrough in an exhibit of military rocketry at the Smithsonian National Air and Space Museum, a temple of aerospace lore where tradition has called for bland captions on horrifying instruments of war.

But a recent visit revealed that on one exhibit a striking change has been installed without fanfare. It's the exhibit of the terror weapon Hitler unleashed in the finale to World War II, the V-2 rocket, which killed thousands of civilians in France, Belgium and Britain.

Unlike the old descriptive material, new captions make it clear that the V-2 was an indiscriminate instrument of murder. Dramatic photos show the V-2's creator, Wernher von Braun -- a postwar architect of the American space program -- briefing a group of uniformed German officers. One photo shows corpses on an Antwerp plaza, victims of V-2. Another shows the slave factories in which the missile was produced. The new explanatory material is striking in comparison to the fairy tale it has replaced on the captured V-2 that has stood on the main floor of the museum since 1976.

Located in a section devoted to civilian space activities, the V-2 on exhibit resembles nearby research rockets. Until the beginning of November, the sole accompanying caption deftly skirted the V-2's lethal purpose and history. The emphasis was on aerospace accomplishment, with no reference to Hitler's intent. The V-2 was too inaccurate for hitting military targets. But it fulfilled Hitler's order for a terror weapon against civilians.

Correctly describing the V-2 as "a milestone in the progress of rocket technology," the old Smithsonian caption, in a mere 125 words, noted that "The V-2 represented an advanced level of rocket engine technology which did not exist in other countries. Based on this German accomplishment, intercontinental ballistic missile systems with thermonuclear warheads have since revolutionized strategic warfare."

The old description stated that "The V-2 held the promise of much larger rockets which could fulfill the dreams of pioneers of space flight." The only reference to von Braun noted that he headed the team that developed the rocket. In the only specific reference to the V-2's deadly purpose, the old caption simply said, "Four thousand of these rockets were fired against Allied targets in England and on the Continent in 1944 and 1945." The death toll is not mentioned. The old description concluded on an upbeat theme: "Thus, after World War II, missiles which caused much death and destruction pointed the way to development of rocket boosters for launching satellites."

The new explanatory material is far more extensive and blunt. The old caption said nothing about how V-2s were made. A new one, accompanying a photo of an immense and gloomy underground factory, states: "Concentration camp prisoners built V-2s under unimaginably harsh working conditions. Thousands perished in the process."

Another caption states: "More than 1,500 V-2s hit southern England alone, causing over 2,000 deaths. ... V-2s killed a total of 7,000 people and terrorized millions." A photo of von Braun is not far from a photo of V-2 victims sprawled dead in the Antwerp plaza.

The new captions do not neglect the technical aspects of the V-2, which was an important milestone in the evolution of space technology. In fact, alongside the grisly aspects of the V-2, the new descriptive material provides far more technical detail about basic technology and significance in space history.

The V-2 labeling change -- the only one of its kind so far at the museum -- reflects a maturing trend toward historical accuracy, according to the person directly responsible for it, David DeVorkin, an aerospace historian. "When I decided to do it," he explained, "a few people winced, but they also said, 'You've got to do it.' There was no hassle about it," he said.

DeVorkin said there was no explicit directive from on high to encourage the labeling change. But he recalled that when the director of the Air and Space Museum, Martin Harwit, was a candidate for the job, he met with the staff. "In discussing our World War II exhibit," DeVorkin said, "Harwit remarked, 'I don't see anything about Dresden' " -- a reference to the destruction of that German city by American and British bombers in militarily purposeless air raids on the eve of the war's end.

Now in painstaking preparation is an ambitious exhibit on World War II strategic bombing, a subject of passionate debate about the morality and military effectiveness of bombing civilian populations.

Meanwhile, more relabeling remains to be done at the Air and Space Museum. A good starting place would be the post-Cold War display of a Soviet SS-20 rocket and American Pershing II.

The captions specify their dimensions, range and TNT equivalents, but nowhere is it explained that these sleek creations of technology are weapons of mass destruction.

The writer is editor and publisher of Science and Government Report, a Washington-based newsletter.