Tracking The Intro of Continuing Characters in DC's Former One-Shot Mags

For most of their history up until about 1959, DC's war and science fiction magazines had not featured continuing characters.  Instead the stories had been one-shots, with characters never returning.  Apparently a decision was reached by management to require continuing features, and very quickly they were put in place:

March 1959: All American Men of War #67 introduced Gunner and Sarge.  The team continued in the next issue, before moving over to Our Fighting Forces, beginning with #45, the May 1959 issue.

April 1959: Sgt Rock made his first appearance in Our Army at War #81 (as Sgt Rocky).

May 1959.  Tank Killer makes his first appearance in All American Men of War #69.

May 1959. The Space Museum opens its doors for the first time in Strange Adventures #104.  It would eventually settle into a rotation with Star Hawkins and the Atomic Knights, with each feature appearing every third issue, until Julius Schwartz turned the editorship reins over to Jack Schiff in 1964. 

August 1959: Mademoiselle Marie, a French resistance fighter, debuted in Star Spangled War Stories #84.

August 1959.  Mystery in Space, which had occasionally had regular features but not for awhile at the time, began running the Adam Strange series, starting with #53.

August 1959.  Space Ranger became the regular feature in Tales of the Unexpected #40.

August 1959.  House of Secrets #23 introduced Mark Merlin, a supernatural detective/debunker.

March 1960. Star Hawkins begins in Strange Adventures #114.

April-May, 1960.  Star Spangled War Stories  publishes the first of many zany War that Time Forgot stories, a series which featured US soldiers battling dinosaurs and other oddball creatures (including a memorable white King Kong).

June 1960.  The Atomic Knights make their first appearance in Strange Adventures #117.

Nov-Dec 1960.  Johnny Cloud, Navajo ace pilot of World War II debuts.

May 1961.  GI Combat #87 hosts the first story featuring the Haunted Tank.

It should be noted that several titles held out even longer; My Greatest Adventure and House of Mystery did not have recurring features until May 1963 (Doom Patrol, #80) and June 1964 (Martian Manhunter, #143).  And of course DC's romance titles resisted continuing characters until Heart Throbs and Secret Hearts began running their soap opera series around 1966.