Bill Post has shared this historical insight in response to a question about the Fog Pressure Units used by the Chicago Fire Department in the early 1960s:
The main purpose of the Fog Pressure Units was to provide a rapid water stream to control fires before traditional engine companies could connect to a hydrant and lay out a canvas line. These units were especially useful in areas where access was limited—such as expressways, alleys, near railroad embankments, or in neighborhoods with poor hydrant coverage and unreliable water supply.
When the Fog Pressure Units were first acquired and put into service between 1961 and 1966, the CFD had only around 11 or 12 engine companies equipped with booster tanks. For nearly a decade—from 1955 to 1966—the department hadn’t bought any new engines. The last batch purchased in 1956 included ten B-model pumpers with 200-gallon booster tanks. A few older engines had been retrofitted with similar tanks, but that was rare.
Each Fog Pressure Unit came with a 300-gallon water tank and two narrow-diameter hose reels. They were fitted with special fog nozzles that created a fine mist at high pressure, which is why they were called "Fog." The first unit was built on a Willys Jeep chassis with a John Bean pump, but the rest used International Harvester chassis with Darley pumps and custom bodies.
While a few units were stationed near expressways, most were deployed in high-risk districts on the city’s west and south sides. Fog Pressure 2 was based at O’Hare Field and originally used the original Willys Jeep unit.
The Fog Pressure Units also served as backup for the Snorkel Squad companies, giving firefighters more flexibility. They could carry extra personnel and equipment. In 1964–65, the CFD added three longer-bodied Fog Pressure units specifically for the Snorkel Squads.
By 1967, when new engines with 500-gallon booster tanks began arriving, many Fog Pressure Units were relocated or retired. By 1970, all but two had been phased out: Fog Pressure 2 remained at O’Hare, and Fog Pressure (SS1A) stayed with Snorkel Squad 1. Most units were taken out of service by 1968–69, including those assigned to Snorkel Squads 2 and 3, which were disbanded in 1969.
As mentioned earlier, Fog Pressure 31A was temporarily assigned to Truck 31’s station for over a year while Engine 64 was being repositioned.
At their peak in 1966–67, there were twelve Fog Pressure units in operation (not counting the three used by the Snorkel Squads). But within two years, almost all were retired, leaving only the exceptions mentioned above.
Bill Post
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