Aberdeen (1784-1860) was one of only two British prime ministers never to serve in the House of Commons (the other was Rosebery). Since the House of Lords was already beginning its long post-1832 decline in importance, this was a significant disadvantage, though his late adolescence was spent under the guardianship of two Commons masters of different types, Dundas and Pitt. Aberdeen’s early career was as a diplomat; he was active in the Sixth Coalition negotiations in 1813-14. He then retired to private life until becoming Foreign Secretary in 1828-30, a post he resumed under Peel in 1841-46. He was an effective, pacific Foreign Secretary, though a poor speaker in the Lords, and followed Peel, to whom he was close, after 1846.
Aberdeen’s government was a coalition of Peelites and Whigs, strong in Ministerial talent, that was effectively reforming in domestic politics. On foreign policy it was split between the pacific Aberdeen and the bombastic Palmerston, who with public opinion behind him wanted to confront Russian designs on Turkey. After the Crimean War began, the inevitable military inefficiencies appeared at first, as in 1793 and 1914-15, for which Aberdeen was blamed, causing his government to fall and be succeeded by a purely Whig government led by Palmerston.
Aberdeen lasted only just over two years but should not be blamed for the Crimean War or be blamed much for the military inefficiencies, inevitable after 40 years of peace. He should be somewhere in the third quartile..