present invention generally relates to drilling a subsea wellbore using a casing string fig1 illustrates a drilling operation of a subsea wellbore with a casing assembly 170 in accordance with the present invention typically most offshore drilling in deep water is conducted from a floating vessel 105 that supports the drill rig and derrick and associated drilling equipment a riser pipe 110 is normally used to interconnect the floating vessel 105 and a subsea wellhead 115 a run in string 120 extends from the floating vessel 105 through the riser pipe 110 the riser pipe 110 serves to guide the run in string 120 into the subsea wellhead 115 and to conduct returning drilling fluid back to the floating vessel 105 during the drilling operation through an annulus 125 created between the riser pipe 110 and run in string 120 the riser pipe 110 is illustrated larger than a standard riser pipe for clarity a running tool 130 is disposed at the lower end of the run in string 120 generally the running tool 130 is used in the placement or setting of downhole equipment and may be retrieved after the operation or setting process the running tool 130 in this invention is used to connect the run in string 120 to the casing assembly 170 and subsequently release the casing assembly 170 after the wellbore 100 is formed the casing assembly 170 is constructed of a casing mandrel 135 a string of casing 150 and a collapsible apparatus 160 the casing mandrel 135 is disposed at the upper end of the string of casing.