The rules for warships in the Suez Canal

In all the talk about the Iranian warships going through the Suez Canal, none of the reports I have seen mention the Constantinople Convention of 1888, which I believe previous post-independence Egyptian governments have endorsed. It is an extraordinary document, in that in theory it gives the warships of belligerent nations (belligerent to Egypt, that is) the right to transit the canal under certain modest restrictions. The extent of the convention's 'generosity' towards belligerents is evident in Article 4:

Vessels of war of belligerents shall not revictual or take in stores in the Canal and its ports of access, except in so far may be strictly necessary. The transit of the aforesaid vessels through the Canal shall be effected with the least possible delay, in accordance with the Regulations in force, and without any intermission than that resulting from the necessities of the service.

    In other words, belligerent vessels do not need to wait and might take on stores 'if strictly necessary'.

    Look at Article 5 too:

In time of war belligerent Powers shall not disembark nor embark within the Canal and its ports of access either troops, munitions, or materials of war. But in case of an accidental hindrance in the Canal, men may be embarked or disembarked at the ports of access by detachments not exceeding 1,000 men, with a corresponding amount of war material.

     There is a let-out in Article 10, which might override the generous provisions in other parts of the convention:

Similarly, the provisions of Articles IV, V, VII and VIII shall not interfere with the measures which His Majesty the Sultan and His Highness the Khedive, in the name of His Imperial Majesty, and within the limits of the Firmans granted, might find it necessary to take for securing by their own forces the defence of Egypt and the maintenance of public order.

    Unsurprisingly, the British government cited Article 10 during the Second World War to prevent Axis vessels transiting the canal and the Egyptian government used it to restrict the passage of Israeli vessels and goods from 1948 until full peace in 1979.
    The Egyptian authorities might have cited Article 10 to deny the Iranian warships the right to pass through, but that would have been rather a stretch since Egypt and Iran have never been at war.
    Part of the $1.3 billion the United States gives Egypt each year in military aid is in return for expedited transit through the canal. In other words, the Suez Canal Authority allows US warships to jump the queue. But since the waiting time for transit is not especially long (more than 24 hours is unusual, I believe, assuming your local agent has done his work), this concession is not as significant as it might appear. The military aid also covers the cost of securing the canal while US warships go through - in other words making sure no one with an RPG is standing on the banks.