Two illustrations from The National Academies for Project Mohole (Credit: Image 1 and Image 2 are both from The National Academies in flickr, CC BY-NC-SA 2.0).

Previous Drilling Efforts on Land and at Sea

Some of the earliest recorded drilling efforts occurred in Northern China over 2000 years ago, where engineers drilled up to 2,000 feet to extract brine, natural gas, and petroleum. The 19th century saw significant advancements in drilling technology during the American oil boom. Techniques originally developed for water wells were adapted for petroleum extraction. In the 1880s, drillers reached depths of 3,000 feet. By the early 1900s, depths of 5,000 feet were surpassed. On the eve of Project Mohole, a few experimental and exploratory wells had reached depths of 25,000 feet.

The transition from land-based to underwater drilling marked a significant evolution in resource extraction technology. Underwater oil exploration began to emerge in the late 1930s and early 1940s, particularly in the Gulf of Mexico. These early efforts laid the foundation for more advanced techniques.

In 1957, the Humble SM-1, a former World War II landing ship  used subsea equipment to drill in an average water depth of 159 ft and with a maximum well depth of 1524 meters (5,000 feet). This was a significant step in drilling technology for shallow water depths. At the time, commercial drilling operations routinely reached depths of 20 to 50 meters.

Technological Limitations and Innovations

Economically viable only for depths up to about 100 feet, stationary platforms were the initial solution for offshore drilling. Engineers innovated as the need to drill in deeper waters grew. The progression from stationary platforms to more advanced floating and submersible systems highlighted the growing complexity of offshore drilling. Project Mohole had to address these challenges head-on, incorporating and expanding upon the lessons learned from previous efforts.

 Choosing the Right Vessel

Selecting and modifying a suitable vessel was essential.  Willard Bascom, Technical Director of Project Mohole, proposed “chartering the best shallow-water drilling ship available and converting it for deep ocean geological drilling.” They found their match in a surplus World War II barge that weighed in at 300 tons and was equipped with a 98-foot drilling derrick. They then set about remodeling the barge to their exacting specifications until it represented the state-of-the art in scientific ocean drilling.

SciOD Spotlight – The Visionary: Willard Bascom

Willard Bascom played a crucial role in convincing the National Science Foundation (NSF) to support the ambitious idea of using large scale, new technology on the CUSS I in order to steady the ship. The goal was to enable the vessel to maintain its position without anchors.

Bascom convinced the NSF to mount thrusters on the CUSS I, a 260-foot experimental marine drilling vessel, to see if they could maintain stability while drilling in 11,000 feet of water.  This would allow the team to drill without a riser, a crucial innovation given the limitations of existing offshore drilling technology. Once NSF was on board, construction and modifications to the CUSS I began in earnest.

Execution of Project Mohole

The CUSS I made three crucial voyages between late February and late April of 1961. The first two trips were short shakedown excursions off the coast of San Diego, allowing the crew to familiarize themselves with the rig and conduct preliminary drills at depths exceeding 3,000 feet.

First Sea Test Mishap: During the initial sea test, a significant mishap occurred when the seven-ton block used for lowering the drill pipes broke loose. This incident nearly tore off the 98-foot tower, highlighting the inherent risks and challenges of deep-sea drilling. Despite this setback, the crew continued their efforts undeterred.

Challenging Weather Conditions: The voyages were conducted under less-than-ideal weather conditions, with cloudy, stormy skies, and waves that made the deck heave and pitch. John Steinbeck, who documented the expeditions in Life Magazine, noted,

“The deck is heaving and pitching. The men step like cats…. We made a pool on the greatest roll and 24 degrees won it.”

Despite 20 to 25 knot winds and eight-to-10-foot waves, the CUSS I managed to hold its position perfectly, demonstrating the effectiveness of the newly developed dynamic positioning system.

Drilling Success and Scientific Discoveries: On Easter Sunday, April 2, 1961 the crew’s efforts were rewarded with the retrieval of a significant core sample. Steinbeck described the moment:

“When the core comes up and is pushed out into plastic cases, the whole crew crowds around—cooks, seamen, drillers, off-duty engineers, scientists.

The excitement culminated in the extraction of a core of basalt, dark blue and very hard, with crystal extrusions,…beautiful under the magnifying glass.”

Project Mohole Achievements

Depth and Precision: Five holes were drilled, with the deepest reaching 183 meters (601 feet) below the sea floor in 3,600 meters (11,700 feet) of water. This achievement was groundbreaking, not due to the depth alone, but because it was accomplished using an untethered platform in deep water.

Core Samples: The core samples were invaluable, penetrating through Miocene-age sediments with the lowest 13 meters consisting of basalt. This confirmed the properties derived from seismic studies, marking a major scientific accomplishment. Recovering subseafloor basalt was so significant that it inspired a congratulatory telegram from U.S. President John F. Kennedy.

Public and Political Support: The successful drilling operations and the subsequent scientific discoveries garnered enormous public interest, largely fueled by a prominent article written by John Steinbeck in Life magazine. Steinbeck’s vivid and enthusiastic accounts of the exploratory drillings captivated the public imagination, significantly boosting support for Project Mohole. In 1962, this wave of public and scientific enthusiasm culminated in Congress voting to back the project with an appropriation of more than $40 million. This financial support underscored the project’s perceived importance and potential for scientific advancement.

Technological Innovations: Project Mohole not only demonstrated that drilling into the Earth’s mantle was possible but also led to the development of several key technologies, most notably dynamic positioning. This system, which allowed the vessel to maintain its position without anchors, became a standard in the oil and gas industry and other marine operations. Phase One of Project Mohole succeeded in proving that both the technology and expertise were available to drill into the Earth’s mantle. It was an experimental phase that drilled to a depth of 601 feet below the sea floor, setting the stage for more ambitious future endeavors.

Legacy and Aftermath of Project Mohole 

Project Mohole was a pioneering scientific and engineering effort that sought to drill deeper into the Earth’s crust than ever before. Despite not reaching the mantle, the project was a resounding success in many ways, setting the stage for future deep-sea exploration and drilling endeavors.

Contributions to Science and Technology

Project Mohole showcased several groundbreaking engineering and operational features:

• Dynamic Positioning: The project proved that dynamic positioning, using controlled propulsion instead of anchors, was an effective means of keeping a drilling vessel stationary for extended periods. This technique became a standard in offshore drilling and other marine operations.
• Stability of Drilling Platforms: It was demonstrated that a ship heading into the principal swell could serve as a stable drilling platform.
• Pressure Maintenance: The project showed that constant pressure on the drill bit could be maintained with the proper combination of drill collars and bumper subs.
• Core Retrieval: The combined use of diamond bits and wire-line coring produced satisfactory core samples from both bottom sediments and rocks.
• Casing Techniques: Casing the upper 200 feet of a hole allowed drilling to significant depths without cuttings falling back into the hole.
• Geophysical Measurements: Standard logging techniques were successfully used to obtain geophysical measurements in the hole walls’ strata.
• Management of Ocean Currents: It was found that oceanic currents posed less trouble than anticipated.

The Impact Beyond Immediate Science and Technology Goals

The project demonstrated the viability of drilling at extreme depths, generating invaluable scientific data and insights into the Earth’s ocean crust and structure, and contributing significantly to the understanding of plate tectonics. Project Mohole also provided a model for perseverance, innovation and interdisciplinary collaboration. It inspired subsequent endeavors such as the Deep Sea Drilling Project and the Integrated Ocean Drilling Program (IODP). Not least, it spurred public interest in scientific exploration through high-profile media coverage, including a 1961 Los Angeles Times’ article that likened the scientific venture to exploring “inner space,” and John Steinbeck’s LIFE magazine article with its descriptions of the basalt extracted from a core as “more precious to me than any jewel could be.”

The Aftermath and Phase II

Despite the groundbreaking achievements,  the CUSS I had its limits. The ship was built as an experimental vessel to test drilling apparatus and techniques, not to reach the Moho. Penetrating the basalt layer between the crust and the mantle required much more rugged equipment than what was available. The vessel also lacked the capacity to store extensive pipe lengths needed to drill six miles down.

The success of the initial phase led to plans for Phase II, involving the development of a new vessel (CUSS II) to reach the Moho.

In February 1962, the NSF announced Brown & Root of Houston, Texas, as the prime contractor for Phase II. However, the project’s expansion faced serious challenges that ultimately weakened its political support.

Concerns arose about alleged political influence on the project’s management and the NSF’s ability to adequately manage such a large and complex undertaking. The  scientific community worried about how the money was being spent.  Cost overruns drew attention from government auditors and gave critics in Congress a compelling reason to defund the program. The initial estimate by the AMSOC committee for the Phase I drilling program was $522,550. The total cost of the program was ultimately estimated to be over three times as much.

“in the original instance, I did not oppose the scientific objective of Project Mohole. What I have opposed is the mismanagement and lack of knowledge which has cost the taxpayers of this country many millions of dollars and will cost them many more millions of dollars before we are through.” Republican Senator Gordon Allott of Colorado declared in an August 1966 Senate floor debate.

In September 1966, Congress killed funding for Project Mohole. Nonetheless, the scientific vision persisted and the equipment was put to good use on other projects. 

View this video to learn more about the preliminary research and preparations made prior to Project Mohole.

References: All of the John Steinbeck quotes are from the following:

Steinbeck, J. (1961, April 14).  High Drama of Bold Thrust through Ocean Floor. Life Magazine, p. 110-122.