['Hamas' Jenkins]

Here was my plan that I wrote up on the BioWare forums for how to engage them:

Send in a scout fleet to zoom by Earth, drawing fire but trying to pull off some ships in a chase to weaken a flank.

The next thing I would do is recommend targeting the entire opening salvo on a Reaper flank. Rather than distributing the fire all around, angle the ships in a way (you have 3 billion miles to figure your angles out if you use scout ships) that allows you to weaken their left or right, increasing your chances for a partial encirclement.

I'd hold back a small contingent of Forlorn Hope evenly taken from each species, save for the Volus and Elcor who are numerically too small, to go directly into the teeth of the Reaper fleet after their attention has been drawn to whichever flank we attacked. These ships would be armed with dozens of nuclear weapons that they would seed amongst the fleet, which would detonate within their lines, hopefully causing mass confusion and some damage. If they turn to address these massive explosions, the main force can try to further outmaneuver the main Reaper contingent, again fighting them in smaller groups with a numerical superiority.

I think that you have to fight the battle where you have, or could conceivably have, tactical advantages. We know that a single dreadnought cannot take down a Sovereign class Reaper. However, it may be fair to assume that a dreadnought would at least be an equal match for a Destroyer, provided that the dreadnought destroyed on Earth in a 1-1 matchup was a bit of an outlier.

If that's the case, I think that you could target and destroy a large number of their destroyers. That should help remove a lot of their tactical flexibility, as they are the true shock troops in their invasions and make up the numerical bulk of the fleet.

Avoid head to head matchups wherever possible.

IMO, ships escorting Hammer forces into London should drop thermobaric weapons a safe distance from Command FOB, but enough around the city to wipe out a large amount of the Reaper ground forces. Such a weapon wouldn't destroy the beam, but would likely incinerate all Reaper soldiers it came into contact with.

Infiltrators and Geth Hunters should act as paratroopers to try and make it to the beam first, as they have the element of surprise. Avoid direct contact and you may be able to slip in largely undetected.