Late in the filming of the second season, Richard Basehart fell ill during the filming of the episode "The Monster's Web" and was unable to complete that episode and work in the next two. "The Monster's Web" was rewritten to minimize the part of his character, Adm. Nelson (knocked out of action in the first act), with a stand-in used for many shots with the face hidden and lines dubbed. The next episode, "The Menfish", had Nelson away and his lines reassigned to guest character Adm. Park (Gary Merrill). The following episode, "The Mechanical Man", had Nelson still away and reassigned his lines to Capt. Crane (David Hedison) and Crane's lines to Cmdr. Morton (Robert Dowdell). Basehart returned in time to appear in the season's last episode, "The Return of the Phantom."