Mittry Mole

tunneling machine

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June 30, 2026

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The "Mittry Mole" refers to an early tunneling machine, specifically the first successful modern tunnel boring machine (TBM). Developed by James S. Robbins and initially contracted by F.K. Mittry, this machine achieved success in 1954 at the Oahe Dam in South Dakota.1

These machines, often called "moles," revolutionized tunneling by significantly increasing excavation speeds, from previous rates of 25 to 50 feet per day to several hundred feet per day. The Mittry Mole and subsequent designs excavate earth with drag teeth and move the material onto a conveyor belt, often operating within a protective shield. Various types of moles have been developed, including open-face and closed-faced wheel types, pressure-on-face machines, and digger-shield types, each suited for different ground conditions.12

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tunnels and underground excavations
Machine-mined tunnels
…of the first machine—the “Mittry Mole.” Later contracts developed three other Oahe-type moles, so that all the various tunnels here were machine-mined—totaling eight miles of 25- to 30-foot diameter. These were the first of the modern moles that since 1960 have been rapidly adopted for many of the world’s…
Read More
…of the first machine—the “Mittry Mole.” Later contracts developed three other Oahe-type moles, so that all the various tunnels here were machine-mined—totaling eight miles of 25- to 30-foot diameter. These were the first of the modern moles that since 1960 have been rapidly adopted for many of the world’s…
Read More