The most important of John Rennie's undertakings, from 1824, was the construction of
London Bridge, the designs for which had been prepared by his father. The bridge was opened in 1831, when Rennie was knighted, being the first of the profession since Sir
Hugh Myddleton to be thus distinguished. He was responsible for the New
River Ancholme Drainage Scheme in
Lincolnshire, and
Horkstow Bridge, which he designed to cross the river at Horkstow in 1835–6, is one of the earliest
suspension bridges to survive and remains substantially as designed. As engineer to the
Admiralty, a post in which he succeeded his father, he completed various works at
Sheerness,
Woolwich,
Plymouth,
Ramsgate, and the great breakwater at
Plymouth, of which he published an 'Account' in 1848. Many years of his life were spent in making additions and alterations to various harbours on different parts of the coast, both in England and in Ireland. One example would be his work in the 1850s designing a
drydock for
Joseph Wheeler at his
Rushbrooke yard in
Cork. He completed the drainage works in the Lincolnshire fens commenced by his father, and, in conjunction with
Telford, constructed the
Nene outfall near
Wisbech (1826–1831). He also restored the harbour of Boston in 1827–8, and made various improvements on the
Welland. He also re-modernised the
Chatham Dockyards in 1862. Creating 3 huge basins and passageways. == Railway engineering ==