can be the type of structures disclosed in u s pat no 3 851 491 the bell is constructed so that it is buoyant that is has a positive buoyancy so that if unconnected to other equipment it moves upwardly toward the sea surface the bell itself includes an outer shell 56 having a hatch 56 for ingress and egress to the life support and working chamber this hatch 58 can be provided with a window for observation if desired an actual observation window 60 is provided on the side of the bell which faces the bop and other such windows can be provided at multiple locations such as at port 62 a penetrator 64 is provided to which the umbilical 90 is connected in order to provide air electrical connections and communication means as well as other types of information and signals which are needed from the bell to the surface during operation ascent and descent in addition to providing for voice communication the umbilical provides for television communication and for the sensors and gauges in the bell to transmit indications to the surface so that some of the controls can be operated and maintained and continuous surveillance performed from the surface the side of the bell facing the bop is provided with manipulators 28 including extendible manipulating arms 66 pivotally connected to the bell and extensible and rotatable and may have for.