The process in which neuroepithelial cells in the neural tube acquire specialized structural and/or functional features of somatic motor neurons. Somatic motor neurons innervate skeletal muscle targets and are responsible for transmission of motor impulses from the brain to the periphery. Differentiation includes the processes involved in commitment of a cell to a specific fate. [ GOC:jid GOC:cls http://www.ncbi.nlm.nih.gov/pubmed/11262869 GOC:dgh http://purl.obolibrary.org/obo/go/references/0000021 GOC:dph ]