Here is one of the “supply” ships. (Pawnee)
That is a war ship. as is the next photo you have displayed, uniformed sailors and cannon make that obvious to all.
the civilian charter Baltic was the “supply ship” for the expedition. She was not armed either. Nor were the other two steam tugs again both civilian charter.
The tug Yankee was not armed at the time of the Sumter expedition, she was a civilian charter, commanded by a Civilian master and manned by civilians. Shortly after her Sumter charter was ended, she was purchased by the U.S. Navy
Within a month of becoming USS Yankee,she was modified to carry two naval 32 lb. guns on her deck.
So was Powhatan, and so was "Harriet Lane." Thomas Freeborn was also known to be armed in the later part of April, but you make a good argument that it might not have been armed on April 12.
Yes, the bulk of the ships consisted of WAR ships, not cargo ships.
the civilian charter Baltic was the “supply ship” for the expedition. She was not armed either.
A couple of hundred riflemen on board constitutes a military mission, and it also constitutes "armed", though not with ships cannon. Perhaps it even had some of those, but it was intended as a troop carrier.
Still a belligerent. Also some of that cargo was munitions.
Point is, they sent ships that would be regarded as a threat. They did not send "cargo" ships, they sent warships and one passenger ship carrying troops and munitions.
A further point is, the Confederates did not know if this was all that had been sent. Other ships were unaccounted for, and the fleet could have been bigger than the Confederates then knew.
But one thing any reasonable person on those shores would know. Lincoln wasn't going to send a group of warships that would be too small to do the job. Lincoln was not going to send ships to be destroyed by the Confederate cannon batteries lining the shore.
But he did. His force was way to small to face what it was expected to face. If it had done what it had been ordered to do, all those ships would have been lost.
Don't take my word for it. Union Admiral David Dixon Porter said this exact thing in his memoirs.
But for some reason all those ships were halted, and prevented from going into harms way, and the official explanation claimed is faulty orders to the Powhatan. A mix up you see.
Astonishing coincidence the mix up caused all those ships to be saved, but still allowed them to be seen by the Confederates as a serious threat.