The title announces the fact that this is going to be a commemorative poem, specifically for the dead Union soldiers. What we don't know yet is how complicated the title is going to be in relationship to the poem. For example, this dedication doesn't go the typical memorial route of straight-up praising the brave and heroic veterans. It's much more complicated than that. It throws in all this stuff about aquariums, outer space, and Boston that doesn't seem directly related to the title.
In fact, the poem does that doll-inside-a-doll-inside-a-doll thing. Every new layer reveals something a little different while still remaining part of the whole. All of these seemingly different things reflect a present day that lives as a result of the Civil War. So everything—from the aquarium to the construction to the schoolchildren—exists in the wake of the Union Dead, whether or not anyone chooses to acknowledge the fact.
There is comparatively little air time given to the actual memorial. Don't get us wrong, it's in there—but under the many layers Lowell creates to make this a rich and complex poem. We like to think of it as a dedication poem, once removed—what we thought was a pretty straightforward title at first read takes on more varied meaning as we work our way through the poem.