In March 1961, off Guadalupe Island in 11,700 feet of water, a converted Navy barge named CUSS I did something humans had never done: it held position in the open ocean using four steerable outboard motors controlled by sonar beacons on the seafloor, and drilled five holes into the Pacific crust. The deepest reached 601 feet of basalt below the mud line. John Steinbeck wrote the cover story for Life. Project Mohole had begun, and its goal was the most audacious in the history of geology: drill straight through the oceanic crust and pull up a piece of the Earth's mantle.

The science was clean. The Mohorovičić discontinuity — the "Moho," named after the Croatian seismologist who identified it in 1909 — is the seismic boundary where compression waves abruptly speed up from ~6 km/s to ~8 km/s. Under continents it sits 30–50 km down. Under deep ocean floor, only 5–7 km. Drill the ocean and you hit the mantle at one-fifth the depth. AMSOC (the cheerfully-named American Miscellaneous Society) convinced the National Science Foundation in 1957 that this was reachable.

Phase 1 worked. CUSS I invented dynamic positioning — the technology every deepwater oil rig and scientific drillship uses today was a Mohole improvisation. Phase 2 was where it died. NSF awarded the $68M Phase 2 contract to Brown & Root in 1962 — a Texas firm with deep ties to Vice President Lyndon Johnson, over the recommendation of NSF's own panel, which favored a different bidder. Congress smelled it. The design ballooned from a converted barge to a purpose-built platform. Estimated costs climbed from $68M to $112M to $127M. In May 1966, the House Appropriations Committee zeroed out the budget. The drillship was never built. The hole was never deepened. Total spent: about $57 million for nothing.

Six decades on, nobody has reached the Moho. The Soviet Kola Superdeep Borehole (1989) hit 12,262 m on land but stalled in 180°C granite at one-third of crustal depth. Japan's Chikyu drillship (2005, $540M) reached 3,262 m below seafloor at the Nankai Trough — impressive, still well short. The IODP's 2015–2016 Hole U1473A in the Indian Ocean hit gabbro near the crust-mantle transition zone but stopped at 789 m due to bit failure.

What's changed since 1966 that makes this finally tractable:

• DP3-class dynamic positioning with redundant thrusters and GPS holds station in 4,000 m of water within 1 m — Mohole-era sonar beacons could manage maybe 30 m.
• Riser drilling with synthetic-fiber risers (under active development by JAMSTEC) eliminates the steel-weight crisis that limited Chikyu to ~4,000 m water depth.
• PDC (polycrystalline diamond compact) bits last 10× longer than 1960s tungsten-carbide tricones in hard basalt.
• Mud-coolers and synthetic drilling fluids handle 300°C+ — the Mohole estimated bottom-hole temperature was 200°C and they had no answer for it.
• Real-time downhole telemetry (Logging While Drilling) means you don't pull pipe to see what you hit.
• Computational modeling of drill-string harmonics in 6 km strings prevents the catastrophic failures that killed Mohole-era runs.

The cost estimate for a Moho-reaching drillship today is under $1 billion — less than two SLS launches, less than one F-35 squadron. The scientific return: ground-truth mantle composition (we've never held a piece of pristine peridotite from in-situ mantle, only ophiolite chunks tectonically shoved to the surface), direct measurement of the seismic discontinuity, samples of the deep biosphere, calibration of every petrological model written since 1909. A single Project Chikyu Mohole campaign would resolve more about Earth's interior than 60 years of indirect seismology.