After taking care of two assignments for Preston, he will reveal a bit more of the Minutemen’s history to the Sole Survivor, and will express his desire to take back their old citadel, referred to as the Castle.
Upon traveling to the Castle, the area is found to be under the control of a rather large group of mirelurks of most variants, which must be dealt with in order to re-secure the area.
The first goal is to take out the nesting mirelurks in the area, both inside and outside of the crumbling fort.
After the mirelurks guards have been dealt with, their egg clusters must be dealt with. While smashing eggs in each egg cluster, 2-3 eggs will hatch in each cluster, forcing the Minutemen and the Sole Survivor to deal with the offspring.
Once a percentage of egg clusters have been dealt with, one of the Minutemen on watch, will alert the group to a large creature swimming towards them from the Castle’s outskirts.
The creature is seen to be a towering mirelurk queen, angered by the death of her children, and she must be dealt with in order to secure The Castle fully.
After dealing with the mirelurk queen, the Minutemen will take control of the Castle’s radio transmitter, which is currently unpowered.
The Sole Survivor will gain access to the Castle as a settlement option, in which they must power the radio transmitter with a large generator in order to progress the Minutemen’s quest-line further.
After the radio transmitter has been powered up, the Minutemen on station will regularly pump out news and updates through Radio Freedom. Regularly listening in on this radio station will update the Sole Survivor with repeatable quests.
Talk to Preston
Meet the Minutemen near the Castle
Preston Garvey thinks it's time for the Minutemen to retake "The Castle", an old fort that used to be their main base of operations. I've agreed to meet him there so we can plan our attack.
Decide on a plan of attack
I've met Preston Garvey and a group of Minutemen near the Castle. We need to agree on a plan of attack.
Wait for the Minutemen to get into position
Preston Garvey and the Minutemen are forming up to attack the Castle on my signal.
Clear the Courtyard
Power up the radio transmitter
The Castle is back under out control. The next step is to get the old radio transmitter powered up.