Complex sentence: He then had to embark on a term of compulsory military service, and spent a year as a sub-lieutenant in the 24th Artillery Regiment, stationed in Tarbes in the Pyrenees.
Split into simpler sentences: He then had to embark on a term of compulsory military service. He spent a year as a sub-lieutenant in the 24th Artillery Regiment, stationed in Tarbes in the Pyrenees.