for example by castellated engagement between upper and lower ends of the shield and the tubular structure above and below the window respectively the tubular structure 112 is rotationally aligned with a branch wellbore to be drilled 122 so that the window 120 faces in the radial direction of the desired branch wellbore this rotational alignment may be accomplished for example by use of a conventional wireline conveyed direction sensing tool not shown engaged with a key or keyway 124 having a known orientation relative to the window 120 other rotational alignment means may be used in keeping with the principles of the invention in fig9 it may be seen that a work string 126 is used to convey a mill drill or other cutting tool 128 a whipstock or other deflection device 130 and an orienting latch or anchor 132 into the casing string 114 the drill 128 is releasably attached to the whipstock 130 for example by a shear bolt 134 thereby enabling the drill and whipstock to be conveyed into the casing string 114 in a single trip into the well the anchor 132 is engaged with an anchoring and orienting profile 136 in the casing string 114 below the tubular structure 112 such engagement secures the whipstock 130 relative to the tubular structure 112 and rotationally orients the whipstock relative to the tubular structure so that an upper inclined deflection surface 138 of the whipstock faces toward the window 120 and the desired branch wellbore 122 thereafter the shear bolt 134 is sheared for example by slacking off on the work string 126 thereby applying a downwardly.