Captain America (vol. 1) #337 (Jan. 1988):
“The Long Road Back”
by Mark Gruenwald, Tom Morgan, Dave Hunt
16 characters in this story:
A few different groups of snake-themed villains have used the name "Serpent Squad." Ultimately, most members of the various Serpent Squads ended up being members of the larger Serpent Society. One "Serpent Squad" was initially organized by Viper in order to infiltrate the Serpent Society. The members of this Serpent Squad were Black Racer, Copperhead, Fer-de-Lance, and Puff Adder. As chronicled in Captain America (vol. 1) #337, these snake-themed villains claimed to be potential new members of the Serpent Society who were trying out for positions in the Society, but when they had their chance, they followed Viper's orders to attack the Society and poison the Society's leader, Sidewinder.
Despite this rather confrontational introduction to the Serpent Society, this Serpent Squad was short-lived, as its members soon saw the benefit of being part of the Serpent Society, joined it, and became longstanding regular members.
This "Serpent Squad" really only appeared in Captain America (vol. 1) #337, because when these characters were next seen, they were part of the Serpent Society.