Paul spotted this photo of a CJ-5 used to navigate the length of the 85-mile Delaware Aqueduct in 1957, still the longest tunnel in the world (construction photos). This was the last time the tunnel was navigate in its entirety. Because of the knowledge gained during their survey, the last living member of this party, Victor Feigelman, was consulted on the state of the tunnel up until his death in 2016.
If you zoom into the area just above gas inlet you’ll note the warning: USE WHITE GAS –ONLY–. The need to limit effluents inside the tunnel also explains the odd exhaust setup.
From Wikipedia, the Delaware Aqueduct … takes water from the Rondout Reservoir through the Chelsea Pump Station, the West Branch Reservoir, and the Kensico Reservoir, ending at the Hillview Reservoir in Yonkers, New York. The aqueduct was constructed between 1939 and 1945, and carries approximately half of the New York City water supply of 1.3 billion US gallons (4,900,000 m3) per day. At 85 miles (137 km) long and 13.5 feet (4.1 m) wide, the Delaware Aqueduct is the world’s longest tunnel.