Unlike other members of the ILB fleet, the D-class (IB1) does not have a rigid hull.

All others with the exception of the Arancia, hovercraft and all-weather lifeboat tenders are rigid inflatable boats.

The very nature of its work requires a swift response, and the IB1 can normally be afloat very quickly.

As of February 2020 the minimum crew for an RNLI IB1 was raised from 2 to 3.

Some Independent Lifeboats have different crewing levels to the RNLI.