The forts on the Asia Minor side of the straights were take by the French. The Fleet would have been able to steam through. Constantinople would fall because it would have a large number of very large guns pointed at it. Whether that would knock the Ottomans out of the war I don't know, but baring a revolution I think not. It could have the opposite effect. Whether the fall of Constantinople would end the fighting in European Turkey again I suspect not. Even if the military is mopped up I would expect there to be an insurgency to deal with.
About the highlightened sections :
The forts :
Any reference for the french haven taken these forts ? I couldn't find it mentioned at least in wiki.
I was refering more to the batteries deeper inside the dardanells
Still a spitroot running IMO.
Not to forget the most likely constantly ongoing mining ITTL of the Dardanells east of Nagara.
Can't see the "steming through" being easily achieved, rather a quite costly buisness for the entente sailors.
The "guns" at Constantinople :
Found an article of swiss origin from 1905 stating, that at that point there were "72 modern Krupp-guns" in battery ...
Therefore I would assume in 1914 there would be at least these guns shooting back, with high-angle plunging fire against rather flimsyly deck-armored old and older entente BS uncapable of high-angle fire and rather unsuited to land bombardement.
Here's the "more to come" ... though
@Peg Leg Pom has essentially already said it :
Fall of Constantinople doesn't kick the Ottoman Empire-now-reduced-to-coreTurkey out of the war.
=> very bloody, very dirty, lots of troops binding, ongoing guerillia warfare in unforgivingly, unknown countryside, without infrastructure to speak of the entente forces are used too (opposite to the turks) by even more nationalized Young Turks.
Not the brightest outlook for middle-class, middle-school, middle-england Kitcherners Army boys.
Don't get me wrong : ofc it's possible for the entente to take Constantinople ... somewhere around novembre/decembre at very, VERY best, but only at the costs of too many troops needed IOTL elsewhere :
in Macedonia and not to forget on the french fronts. ... with an awfull lot of other butterflies there.
No ammo for Serbia, as the MEF and ANZAC would use up every shell they get a hand on (what they would have to).
Leaves the possibilty of taking the Gallipoli penisula and ... let it be good with that. That would have achievd :
nothing
- no ammo for Serbia (again, see above) so Serbia's still defeated
- shipping neither to nor fro Russia via the Black Sea
- still no pressing reason for Bulgary to join the entente
but a great booldshed ending in a stalemate trenchwar at the fortress line at Muriar Dere at the neck of the peninsula (at any point in time you wish), what could still count as a strategic, at least propagandistic victory for the Ottomans having beaten back 2 Great Powerss assault, that achieved nothing.