Natick Labs was directed to create a spike-protective insole for the jungle boot in order to combat the injuries suffered by soldiers treading on poisoned Punji stakes and contaminated spikes. Their initial offering, a slip-in stainless steel insole, was sent to Vietnam in 1963 but tended to cause blistering.
As result, in early 1966 Natick redesigned the DMS Tropical Combat Boot with an integral spike-protective insole that successfully eliminated the fitting and blistering problems.1 The spike protective boot also had 2-inch wide nylon webbing ankle supports in addition to the 1-inch nylon webbing reinforcements of the top stay and backstay.
Although jungle boots were issued to all personnel, Aircrew were directed to wear leather combat boots because of the danger of the nylon uppers melting in cockpit fires.1. Support To United States Army In Vietnam - Clothing & Equipment (United States Army Material Command Feb 1967)