Complex sentence: In May 1747 he was posted on a temporary mission "solely for military matters" to the Republic of Genoa, before being posted, some weeks later, to London by the new Spanish Minister of State, José de Carvajal and a friend of Huescar.
Split into simpler sentences: In May 1747 he was posted on a temporary mission "concerning only military matters" to the Republic of Genoa. He was then posted, some weeks later, to London by the new Spanish Minister of State, José de Carvajal, a friend of Huescar.