Complex sentence: In 1917 he was attached to the Russian army in Romania, and was promoted temporary lieutenant-colonel in January 1918 and brevet lieutenant-colonel in June 1918, and for the next two years he served on "special duty" in Russia during the revolution.
Split into simpler sentences: In 1917 he was attached to the Russian army in Romania, was promoted temporary lieutenant colonel in January 1918, and brevet lieutenant colonel in June. For the next two years he served on "special duty" in Russia during the revolution.