Abstract: A sub-sea well head comprising a connector and a christmas tree which is enclosed in a capsule is characterized in that a master valve is contained within a member forming the foot of the christmas tree, the member penetrating and being sealed into the bottom of the capsule and supporting the capsule, and in that the master valve is contained within a part of the member within the capsule.

Abstract: A capsule for enclosing a sub-sea installation part is intended to be left water-filled and thus means for sensing oil or gas leaks from the part is disposed in the upper part of the capsule to where such leakage will float.

Abstract: A sealing arrangement between a transit capsule and a sub-sea capsule comprises a member(secured and sealed to the sub-sea capsule)which seals to the transit capsule but can be disengaged from the sub-sea capsule and carried by the transit capsule to the surface for repair of the seal between the member and the transit capsule. Means are described to ensure that the seal between the member and the sub-sea capsule is reliable.

Abstract: A transit capsule for providing operator access to a sub-sea installation part in a capsule on a sea-bed, the two capsules having complementary means to form a conjunction capsule, has means selectively connecting an expansion vessel in the transit capsule to the other two capsules; on connecting the said other two capsules which are water-filled, their pressures are reduced to the atmospheric pressure in the transit capsule with only a small amount of water being ejected to balance the pressure and this small amount can be inspected to determine the state of the said other two capsules by suitable inspection means.