A Dutch-built tugboat, the Knocker White (originally called the steam tug Cairnrock) was built in 1924 by T Van Duijvendijk’s yard at Lekkerkek near Rotterdam, Netherlands for Harrisons (London) Lighterage Ltd.

Following the installation of a steam engine and boiler at Great Yarmouth, the steel-hulled Cairnrock – which was designed for general towage work and featured a drop-down funnel for travelling under bridges – was initially used to Tow the Harrisons’ floating steam-powered coal elevator Wotan around the lower reaches of the Thames. 

In 1960, the 77 foot long tug was sold and passed through the hands of a couple of different owners and ended up, by 1962, in the hands of WE White and Sons. It was during this time that its name was changed (after a White family nickname), marine diesel engines installed and the steam engines and boilers removed.

The Knocker White continued in service, operating out of the WE White & Sons base at Hope Wharf in Rotherhithe, working on the Thames and the Solent until 1982.

In November of that year, it was sold for scrap to Todd (Breakers) Ltd of Dartford but, after being drawn to the attention of the Museum of London, was acquired by them in March 1985 as a classic example of an early tall-funnelled Thames steam tug.

In November, 2016, the Knocker White – along with the Varlet – was acquired by Trinity Buoy Wharf with the aim of restoring the vessel and putting on public display. It can be seen moored at the wharf today.