[1][2] McClennan had gone to medical school after being the second African American appointed as a midshipman to United States Naval Academy.

Orphaned when young by his mother's death, he was raised after the Civil War by his uncle, Edward B. Thompson, a free black barber.

He was later appointed as a legislative page in the South Carolina state legislature with the help of another uncle, Samuel B. Thompson, a Republican representative.

[5] After Cain was elected as United States Representative for South Carolina's at-large district, he resolved to make appointments to the service academies.

[9] Four years after graduation from medical school, McClennan moved to Charleston, South Carolina, where he established his practice and gained an "excellent reputation as a physician".

[12] The Hospital and Training School for Nurses was chartered by the South Carolina legislature in July 1897, and opened with 24 beds in a three-story building purchased for $4,500 (equivalent to $164,808 in present-day terms).

[2] Funds for the purchase of the building and necessary equipment were secured almost entirely by local charity, including support from the Duke Endowment.

[13] McClennan married Ida Veronica Ridley, a schoolteacher from a prominent African-American family in Augusta, Georgia.