How did the Earth Force captain know the Minbari cruiser had its weapons ports open?

Question

The Babylon 5 TV movie, In the Beginning, shows how an Earth Force captain started the war with the Minbari.

The Minbari Grey Council, led by Dukhat, have become concerned that the Shadows may have returned to Z'ha'dum in fulfillment of Valen's prophecy. They are taking a roundabout route to investigate when they encounter Earth ships, specifically the Prometheus, seeking to investigate the Minbari.

The Minbari ships turn toward the Prometheus and engage their long-range sensors to gain more data on the unknown Earth ship. Unknown to the Minbari, the intense EMP field generated by their sensors disables the Prometheus' jump engine, preventing the Earth ship from retreating. As the Minbari ships draw closer, they open their gun ports—a sign of respect in their culture. The interference from the Minbari sensors also prevents the Prometheus from determining whether or not the Minbari ships are charging their weapons. The captain of the Prometheus, with his jump engines disabled and the Minbari ships approaching with apparent intent to fire, misinterprets this as a sign of aggression and opens fire. The Minbari ships are heavily damaged, and Dukhat is killed. In retaliation, the Grey Council declares a holy war against humanity, and the Earth–Minbari War begins.

How did the captain know the open ports were for weapons?

The open ports could have been for sensor equipment. Or for docking arms. Or for creating jump gates. Or some technology beyond what humans know.

The point is that the captain could not know since this is the first contact with the Minbari. He does not know Minbari ships. He does not know Minbari technology.

Answer 1

In the episode B5: Legacies we see a similar situation. A Minbari War Cruiser approaches with "gun ports open". The sensors scan the vessel and determine that she's "armed for a fight". The still from the sensors indicates that not only are the weapon ports open, but that the guns themselves are charged and ready to fire.

It can be assumed that the technology involved in the earlier conflict is sufficiently similar to Earthtech for them to be immediately recognised (by sensors) as guns.

Perhaps it would have been more accurate to say

"With gun ports open [and there appears to be a power surge in the area near the guns.]"

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JMS spoke to this issue in his commentary on the book Clark's Law by Jim Mortimore. In short, there was certainly lot of guesswork going on on behalf of the Earthforce sensor teams but that they could clearly determine that these were guns from their profile.

Why did the captain lie?

The Minbari approached with their gun ports opened...but they also hadn't locked on. They were a potential menace, but had not gone into the territory of definite menace...and when they fired, it was clear from the moment or two it took to respond that the Minbari ships weren't ready to attack. So he chose to cover his butt rather than take responsibility for screwing up a first contact situation and plunging Earth into a war.

Answer 2

I think this question is like, "How can the Enterprise know that there are life signs on a planet?"

In the majority of Science Fiction - Babylon 5 included - we aren't told how every piece of technology works - suffice it to say that the Earthforce's ship's computer's A.I. has the capability to identify a weapon at least to a high degree of probability - even if it has never encountered this type of ship before.

Like: a person from a primitive society might never have seen a sword before and see someone facing them menacingly with a length of sharp metal. Even though it could be for cutting trees or drawing pictures in tough dry soil, they could probably guess it's a weapon.