Why the Allied fleet became inadequate by April

Did Allied planners misunderstand the Ottoman ability to resist naval attack?

Not entirely; their force was adequate early, but Ottoman defenses strengthened by April while the Allied commitment did not increase enough.

Allied planners understood Ottoman resistance but expected their naval firepower to overpower it. That judgment was plausible in February and still defensible in March, when the forts and garrisons remained vulnerable. By April, Ottoman defenses had improved while the Allied force had not grown enough to match the changed problem. The comparison shows why operational delay must be paired with force reassessment rather than assuming yesterday's plan remains adequate.