They're about the size of a medium dog, if you were to create a box that touches the ends. They're much skinnier though. Which means that they have a higher surface area for their mass, which means more armor.
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Science vessals don't look much like they'll be any bigger than half a BC in real life. Battlecruisers are like 1 or 2 times the size of the Colossus or Sathanas in Freespace 2, which is very, very, VERY big.
No. A science vessel is probably about the same size. Watch the cinematic, they're huge.
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I only remember marine: 5 feet tall.
5 feet?! I'm sure you have that wrong...
5 feet is shorter than a 13 year old... I'm 5"3...
It's probably slighter taller than the Master Chief would be, because
their armor is way more massive- more like a Clan Elemental or a Heavy Gear than a combat armor...