The D-class lifeboat (Avon S650) was a sub-class of 4 inflatable boats operated as part of the D-class between 1971 and 1986 by the Royal National Lifeboat Institution of the United Kingdom and Ireland.

[1] For more than 60 years the D-class has served as the workhorse of the RNLI Inshore Lifeboat (ILB) fleet.

The D-class was specifically designed as a light and highly manoeuvrable rapid response craft, especially suited to close shore work.

There were only 4 Avon S650 boats in service with the RNLI The D-class lifeboat consists of two sponsons, together housing four inflatable segments intersected by baffles.

Unlike other members of the ILB fleet, the D-class does not have a rigid hull; all others, with the exception of the Arancia, hovercraft and ALB Tenders, are Rigid Inflatable Boats (RIBs).