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U.S. Nuclear Commander Stands By "Vacuum Tube" Rationale for Updating Arsenal

By Elaine M. Grossman

Global Security Newswire

(May. 14) -The head of the U.S. Strategic Command last week defended using the issue of aging vacuum tubes, used in B-61 gravity bombs, in making his case for modernization of the nation's nuclear arsenal (U.S. Navy photo). (May. 14) -The head of the U.S. Strategic Command last week defended using the issue of aging vacuum tubes, used in B-61 gravity bombs, in making his case for modernization of the nation's nuclear arsenal (U.S. Navy photo).

WASHINGTON -- The top U.S. combatant commander for nuclear weapons last week defended his use of vacuum tubes as a tangible prop for arguing that the strategic arsenal must be modernized, despite complaints that his pitch is misleading (see GSN, Sept. 12, 2008).

Gen. Kevin Chilton, who heads U.S. Strategic Command, on occasion has cited the continued employment of 1950s- and '60s-era vacuum tubes in the nation's nuclear weapons to illustrate his concern that the aging stockpile might become less reliable.

In one instance, the Air Force general late last year brought such a device to a meeting with the Wall Street Journal. Chilton told the paper that a congressional prohibition on spending funds to develop a new Reliable Replacement Warhead prevented the Energy Department from studying how a vacuum tube in the B-61 gravity bomb could be replaced by a computer chip.

However, two nuclear security experts recently took issue with his remarks, asserting that vacuum tubes "have nothing to do with the RRW debate." Writing last month in the Bulletin of the Atomic Scientists, Jeffrey Lewis and Kingston Reif argued the devices are "the perfect symbol of technological obsolescence" but also an example of "Chilton's dramatic flair."

Lewis directs the New America Foundation's Nuclear Strategy and Nonproliferation Initiative, and Reif is deputy director of nuclear nonproliferation at the Center for Arms Control and Nonproliferation.

Last week, the strategic commander said Lewis and Reif had misconstrued his point, which he insisted was to call for a broad overhaul in the nuclear stockpile and the complex that maintains the weapons.

"A life-extension program is what we have [had] to do for the last 15 years, and I think it's been successful to this point," Chilton told reporters at a May 7 Defense Writers Group breakfast. However, he said, "I don't think that gets you to where you want to be 20 years from now."

Rather, steps must be taken to "modernize" the arsenal, giving the weapons increased reliability, safety, security and maintainability, he said. Those were objectives of the Reliable Replacement Warhead program, a Bush administration effort that Congress canceled last year.

President Barack Obama's fiscal 2010 budget request, delivered to Congress last week, includes no funds for the RRW project (see GSN, May 11). However, during a speech in Prague last month, the president affirmed that "as long as these weapons exist, the United States will maintain a safe, secure and effective arsenal."

Chilton also called for updating facilities and systems for maintaining the weapons, and attracting "young people into this [field] so that we have the expertise available in this country to sustain the nuclear deterrent."

Still, the Wall Street Journal article reported that Chilton cited the vacuum tube as a specific example of vintage technology that cannot be replaced without an RRW-like modernization program. He left unclear how many of the 2,700 operationally deployed strategic and tactical nuclear weapons in the U.S. arsenal include vacuum tubes, or what purpose the apparatus serves in a weapon.

"Replacing the vacuum tube with a chip isn't going to happen anytime soon. The Department of Energy can't even study how to do so since Congress has not appropriated the money for its Reliable Replacement Warhead program," the paper described the strategic commander as explaining.

Lewis and Reif cast doubt on that notion.

"Vacuum tubes are not used in the physics package of a single nuclear weapon design," wrote the critics, referring to the central nuclear explosive component of a weapon. "Vacuum tubes are used only in the radar-fuse, which tells the firing system when the bomb is at the correct altitude for detonation, in some [models] of one warhead design, the B-61 gravity bomb."

With the vacuum tubes placed outside the bomb's central physics package, neither nuclear explosive testing nor a wholesale modernization is required for them to be monitored or replaced, according to Lewis and Reif.

"The Energy Department has routinely replaced radars without nuclear testing or redesigning the physics package," their article states. "Of the many reasons that defense and energy officials have put forth to justify the RRW program, the need to replace vacuum tubes is the worst and has no place in the debate about the RRW or modernizing the nuclear stockpile."

However, in his comments last week, Chilton suggested the criticism was off-base.

"I think they were confused, frankly," he said of Lewis and Reif. "We are still using vacuum tubes and they are essential to the operation of the weapon."

Asked to clarify whether he differs with the nuclear experts' characterization of the devices as readily accessible for test or replacement, the general instead repeated how important a role they play.

"They are essential to the operation of the weapon, OK?" Chilton said. "The weapon doesn't work without them."

"I think the plain reading of 'confused' is that there is some technical inaccuracy in what we wrote," Lewis told Global Security Newswire this week. "Either Chilton can point out an inaccuracy in what we wrote or correct his own wildly misleading statements to the Wall Street Journal."

The strategic commander is "really obfuscating and making things more difficult," agreed Richard Garwin, a longtime nuclear weapons physicist and IBM fellow emeritus.

"I'm absolutely confident that the vacuum tubes can be replaced if you really needed to replace them, which you don't," he said in a telephone interview Monday.

In testimony before a House panel in March, Garwin said the same approach applies broadly to virtually any component outside the warhead physics package.

"Without nuclear testing, replacement parts outside the 'nuclear package' that contains the weapon primary and secondary [explosive stages] can be replaced by identical, qualified parts; or a major non-nuclear system or subsystem might be replaced by a new-development system that could be thoroughly tested without a nuclear explosion, as was always the case," he told the House Appropriations Energy and Water Development Subcommittee.

"Batteries, fusing systems, radars, can all be modernized, and because the replacements are usually smaller and lighter, they may be accompanied by dead weight to maintain warhead weight and balance," he stated.

Lewis said he suspects Chilton has simply erred in his past citations of the vacuum tube as an illustration of why a full nuclear warhead modernization program is needed.

"If he admits that the vacuum tubes in question are used only in the radar-fuse, he is going to look like a fool," Lewis said. "To say that the weapon doesn't work without them is true, but completely irrelevant."

"I was thoroughly puzzled by Gen. Chilton's responses" to questions last week, Reif added. He said the co-authors share Chilton's concern "about how best to maintain our arsenal as it ages," but "at no point do we argue that vacuum tubes are not essential to the functioning of the radar-fuse in the B-61."

In an interesting twist, some observers offer the view that vacuum tubes might remain preferable to circuit boards in hardened military electronics.

"They are far less vulnerable than integrated circuits to the destructive effects of the electromagnetic pulse generated by nuclear explosions," said Frank Richter of Detroit's World Affairs Council in a December letter to the Wall Street Journal.

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