Police say the alleged assault happened in the early morning hours Friday morning.
Portsmouth police, Special Victims Detectives, and Child Protective Services began an investigation at approximately 1:10 p.m. after Medical staff at NMCP informed them of the abuse.
Agents with Naval Criminal Investigative Services also responded and assisted.
Medical staff reported that sometime between the hours of 1:30 a.m. and 2:30 a.m. the 11-day-old baby boy received bruising to his body, including visible contusions on his back and face, while the baby was in the Neo-Natal Intensive Care Unit.
Police have charged 21-year-old Matthew Wayne Strawn of Portsmouth with one count of felony child abuse and one count of felonious assault.