Complex sentence: London Transport later ordered 27 trains "A62 Stock" trains, introduced in 1961--63 to replace F and P Stocks on the Uxbridge service.
Split into simpler sentences: London Transport later ordered a further 27 trains, which became known as the "A62 Stock". This second batch were introduced between 1961--63 to replace the F and P Stocks on the Uxbridge service.