Every so often, people go on about how Cthulhu isn't all that, given that he was defeated by being rammed by a steamboat.
But Johansen had not given out yet. Knowing that the Thing could surely overtake the Alert until steam was fully up, he resolved on a desperate chance; and, setting the engine for full speed, ran lightning-like on deck and reversed the wheel. There was a mighty eddying and foaming in the noisome brine, and as the steam mounted higher and higher the brave Norwegian drove his vessel head on against the pursuing jelly which rose above the unclean froth like the stern of a daemon galleon. The awful squid-head with writhing feelers came nearly up to the bowsprit of the sturdy yacht, but Johansen drove on relentlessly. There was a bursting as of an exploding bladder, a slushy nastiness as of a cloven sunfish, a stench as of a thousand opened graves, and a sound that the chronicler could not put on paper. For an instant the ship was befouled by an acrid and blinding green cloud, and then there was only a venomous seething astern; where--God in heaven!--the scattered plasticity of that nameless sky-spawn was nebulously recombining in its hateful original form, whilst its distance widened every second as the Alert gained impetus from its mounting steam.
But what's our only source for this? The journal of a freighter's sole survivor, who describes his shipmates having gone mad before dying, at the same time (unbeknownst to him) artists and sensitives were having disturbing dreams all around the world.
R'lyeh never rose. Johansen and his shipmates never encountered Cthulhu.
They were just above R'lyeh while Cthulhu stirred in his slumber. Already disturbed by having been attacked by the Alert, losing the Emma, and having killed the crew of the Alert, the proximity was enough to cause the waking visions that inspired several of them to step out onto a R'lyeh that wasn't there, that caused Johansen to imagine a Cthulhu that could be shattered by a steamboat. By whatever combination of mental fortitude and good luck, Johansen had a vision that didn't inspire him to bring about his own death, and he wasn't wholly shattered by the event.
The stars just weren't right. When they are, a steamboat's not going to help us.