The army is in the process of selecting a new rifle and light machine gun. This report looks at one of the candidates, but also provides links to information about the other candidates. It is probably going to be a while before the Coast Guard sees a replacement for our existing weapons, with the possible exception of the specialized units.
There is also some information on the new 6,8mm (.277″) round designed to be relatively light while having greater range and better penetration of advanced body armor than the 5.56mm (.222″) round.
Might be useful for killing outboards.
Of important note Chuck. The US Army does not intend to replace all of their carbines & automatic rifles with which weapons are selected for the ‘Next Generation Squad Weapons” program. They are earmarked for the combat arms brigade formations. The M4s & M249s will still see several decades of service in the US Army
More information here. https://www.armytimes.com/news/your-army/2019/10/17/how-the-army-is-building-an-unparalleled-rifle-and-saw-replacement-for-soldiers/
Indicates that the Marines will get the 6.8mm too, but not clear if this means all or just some.