The comfort shoe was developed by Natick Labs as part of Operation Safe Step, which began in 1968 with the aim of reducing the incidence of dermatophytosis (foot fungus) suffered by soldiers operating in Vietnam’s inundated areas. During 1967, 9th Infantry Division troop ineffectiveness as a result of fungus disease in the Mekong Delta averaged 40%, which was a higher ineffectiveness rate than all other causes combined, including wounds.
The canvas comfort shoe was designed to eliminate the problem of troops wearing wet boots overnight. The low quarter style exposed as much skin as possible to the air while protecting the feet from mud and rough ground. The British had successfully controlled foot fungus in Malaya by employing tennis shoes in a similar fashion.
Two models were produced by Natick and tested by field elements of the 9th Inf. during 1969:
Type-I - Lace up
Type-II - Velcro fastener with auxiliary eyelets
The Type-II shoes were found to be easier to put on and take off and when laced through the auxiliary eyelets they remained on the feet whilst running through paddy type terrain. Consequently they were type classified as standard A in May 1970 and were issued in sizes 5 to 14. The shoes became known colloquially as night slippers or bivouac booties.11. E247, ENSURE, Records of the U.S. Army Concept Team Activity, Records of the United States Forces in Southeast Asia, 1950-1975, Record Group 472, National Archives at College Park, MD