Rosie McGee was cracking up at her desk when Dennis "Wiz" Leonard walked in from lunch.
"What's the story?" Wiz asked McGee, then a receptionist and bookkeeper at Alembic, a California-based custom electric guitar, bass, and pre-amp company where Wiz worked as an audio engineer.
"Well, the Department of Defense just called me," she told him. "They were asking if we could defer the purchase of our next four 3500s, so they could get four."
McGee was referring to the McIntosh MC3500, a 350-watt tube amplifier. The Mac 3500, as it's widely known, was one of the more efficient amps available at that time, when Alembic was collaborating with the Grateful Dead on the Wall of Sound, a massive hi-fidelity sound system that revolutionized live music. The Wall of Sound would eventually comprise nearly 50 McIntosh amps, a mix of MC3500s and solid-state MC2300s.
Those amps were in high demand at Alembic. The 3500s, in particular, would be used in the Wall of Sound's vocal array tweeters, drum tweeters, and for Jerry Garcia's guitars. But was it just Alembic buying them up? A rumor was going around—a "urban myth," Wiz told me—that the US military was using Mac 3500s for sonar, specifically to listen for Soviet submarines.
Rosie McGee, who confirmed that the exchange with Wiz that afternoon did happen, was told to tell the Department of Defense "no," Alembic would not give up its order.
"We got in the way of the war machine," Wiz later told me.
Psychedelic rock, Cold War-era intrigue—it sounds like something out of a Pynchon novel. I had to get to the bottom of it.
"While nothing was said specifically, hooking them up to power sonar transmitters would be an obvious use."
It's unclear what the US military might have been doing with Mac 3500 amps back then, if in fact it was doing anything with them at all.
In Blair Jackson's Grateful Dead Gear, Wiz said that a McIntosh employee cleared the air over what the military was using Mac 3500s for—to listen for Russian subs—after the project had been declassified. A cursory Google search suggests the military was using McIntosh products in the late 1960s and early 1970s for seemingly banal research into antennas and aviator helmet stability, not sonar, as Wiz claimed.
"The 3500s were being used to drive miles of cable, literally miles, that led to a submersible remote-controlled little baby submarine," Wiz told me. "And it had speakers in it. The guys in the destroyer who were towing this thing, they were doing sonar exercises—sonar ops that were in training on submarines out in the ocean. 'OK, put up the signature of Alpha class,'" Wiz said, impersonating someone running this hypothetical sonar exercise. "'See if they can find it.' They'd have these recordings of Russian submarines, and they'd just play them, drive the cable, and the speakers would emanate the sound of any particular Russian sub that they wanted to put up. And that was actually what the military was doing with these amps."
It sure has a heady, acid-washed ring to it.
When I asked Naval and History Command, a wing of the US Navy, if the Navy used Mac 3500s for sonar in the early 1970s, a representative told me there is no way to verify such a claim, in part because there does not exist an archive of past purchase orders to plumb.
Whether the Navy really was using 3500s while towing big radio-controlled transducers for miles behind destroyers, to play the signatures of different Russian subs, is ultimately a matter of speculation, yet in theory it could have worked.
I contacted Susan and Ron Wickersham, who head up Alembic to this day. They recall a McIntosh rep informing Alembic in 1973 that an initial order of 3500 amps for the Wall of Sound would be deferred in favor of a defense department request.
"There was some mention at the time they were going to be used on submarines," Susan told me. "While nothing was said specifically, hooking them up to power sonar transmitters would be an obvious use. We can't confirm or deny this."
On the surface, at least, she said it was polite of the DoD to ask Alembic to defer delivery of the four 3500s. But at the end of the day the military can supercede anyone's order, which is exactly what happened. The next shipment of available 3500s came through to Alembic 30 days later.
"Were we happy about it?" Susan said. "No, we were not."
"It was McIntosh that delayed our shipment in favor of the much larger continuing client: the DoD," she added. "From McIntosh Lab's viewpoint the amount of gear Alembic would purchase is less than an anthill compared to the mountains the military buys annually."
McIntosh was unable to provide any definitive information about what business, if any, it did with the US military in the 1970s.
Rumors aside, 1973 was a pivotal moment for hydroacoustic surveillance of the oceans.
That year, the Soviet Union rolled out its first fleet of nuclear-powered ballistic missile submarines, which threatened the ability of the US Navy's sound surveillance system (SOSUS) "to fulfill its early-warning detection role," writes Lieutenant John Howard, of the US Naval Postgraduate School, in a history of fixed sonar systems published in 2011. (The US Navy began developing SOSUS, a constellation of underwater listening posts, in 1949 as a way to track Soviet submarines.)
Also in 1973, the US Navy started developing its next-generation ocean surveillance sonar network, the Surveillance Towed Array Sensor System, or SURTASS, which focused on the long-range detection of submarines. SURTASS got underway with the prototype research vessel Moana Wave, which towed an array of hydrophones for miles behind it.
Meanwhile, Alembic was kitting out the Grateful Dead's sound system with McIntosh amplifiers. If it's not beyond the realm of possibility to think the Navy likewise employed this kind of hi-fidelity amplification technology, it's fun to entertain the idea that maybe, just maybe, some of the 3500s amps that were supposed to go to the Dead wound up aboard Moana Wave.
It's still hard, perhaps impossible, to know if the amps Alembic had to defer to the US military were used in some capacity in Cold War-era sonar.
Alembic, for its part, has a long history of selling custom musical equipment to the US government, including the Navy, Susan Wickersham told me.
"The military did purchase directly from me a number of Alembic F2B tube preamps and matching Mac 75 amplifiers," she said. "They were purported to be used for recreational purposes on board some submarines. Playing music in off times keeps the troops happy."
Hell of Salt Water is a series on Motherboard about exploring and preserving our oceans. Follow along here.