Device for watertight connection between two enclosures, comprising: • a first door and a first collar associated with a first of the two enclosures, wherein said first door is movably held by the first collar in particular by a tilting movement around a tilt axis (Y-Y) orthoradial to a central axis of the first collar between a first closed position, in which the first door tightly seals the first collar, and a first open position, in which the first door is spaced from the first collar for access to the first enclosure; • a handle for locking the first door in the first closed position, wherein said locking handle is held by the first collar to be movable, in particular rotatable around a rotation axis parallel to the central axis of the first collar between a position locking the first door in first closed position and a position releasing the door from the first closed position into the first open position; and • a second door and a second collar, which are associated with the second enclosure and which are provided with first elements for reversibly fastening one to the other, wherein said second door is held by the second collar in order to rotate around a central axis of the second collar between a second closed position, in which the second door is fixed to the second collar by the first fastening elements and tightly seals the second collar, and a second open position, in which the second door is disconnected from the second collar for the purpose of access to the second enclosure, wherein the first and second collars (20, 40) are provided with second elements for reversibly fastening one to the other and the first and second doors (10, 30) are provided with third elements for reversibly fastening one to the other such that, during assembly of the first and second collars by centring these collars on a common axis (Z-Z) and by displacing these collars in relation to one another in rotation around this common axis (Z-Z), the first and second collars are fixedly connected to one another by the second fastening elements, the first and second doors are fixedly connected to one another by the third fastening elements and the second door is displaced from the second closed position into the second open position, wherein the connection device additionally comprises a mechanism for locking the locking handle in locking position to prevent the locking handle from shifting from its locking position in the absence of assembly of the first collar with the second collar, wherein said locking mechanism comprises a mechanical operating element, which is held by the first collar in order to be able to perform a translation movement parallel to the common axis (Z-Z) between a resting position, in which the operating element controls the locking of the locking handle in locking position by the rest (81, 82, 83, 84, 86) of the locking mechanism, and an activation position, in which the operating element acts on the rest of the locking mechanism to free the locking handle so that it can be displaced from its locking position into its release position, characterised in that the operating element is held in its resting position under the action of an elastic member of the locking mechanism securely interposed between the operating element and the first collar and is displaced from its resting position into its activation position by application of the second collar onto the operating element when the first and second collars are assembled on one another, counteracting the action of the elastic member. • a first door and a first collar associated with a first of the two enclosures, wherein said first door is movably held by the first collar in particular by a tilting movement around a tilt axis (Y-Y) orthoradial to a central axis of the first collar between a first closed position, in which the first door tightly seals the first collar, and a first open position, in which the first door is spaced from the first collar for access to the first enclosure; • a handle for locking the first door in the first closed position, wherein said locking handle is held by the first collar to be movable, in particular rotatable around a rotation axis parallel to the central axis of the first collar between a position locking the first door in first closed position and a position releasing the door from the first closed position into the first open position; and • a second door and a second collar, which are associated with the second enclosure and which are provided with first elements for reversibly fastening one to the other, wherein said second door is held by the second collar in order to rotate around a central axis of the second collar between a second closed position, in which the second door is fixed to the second collar by the first fastening elements and tightly seals the second collar, and a second open position, in which the second door is disconnected from the second collar for the purpose of access to the second enclosure,