Operation: Grave Digger

Quest pops up automatically when you hit 4500 rep in Friendly on your way to Honored.

For The Honorbound, to be specific. ;)

For the BFA War Campaign, there are 4 breadcrumb quests: Operation: Grave Digger, Operation: Water Wise, Operation: Bottom Feeder & Operation: Hook and Line. They all act in the same way. Originally they would pop up during the campaign, telling you you needed to get more reputation with The Honorbound before opening up next step. However, in 8.2.5, Blizzard removed the reputation requirements for the War Campaign quests. At first I thought that had effectively made these breadcrumbs unavailable, but they can be done, you just have to do things in a very specific manner.

For Operation: Grave Digger:
1) Do all the intro quests from Nathanos, up to and including The Bridgeport Ride.
2) Do not accept next War Campaign quest from Nathos yet.
3) If needed, grind Honorbound reputation up to Friendly 4500/6000. Check https://www.wowhead.com/guide/the-honorbound-reputation-guide-6209 for tips.
4) Triggering the actual quest can be done in two ways: Getting reputation with Honorbound past the required rep (for example by doing a WQ on Kul'Tiras) or by relogging in Orgrimmar.
5) Now you can turn in Operation: Grave Digger and continue on with next step of the War Campaign.

For Operation: Water Wise:
1) Continue on with War Campaign, up to and including What Remains of Marshal M. Valentine.
2) Do not accept next War Campaign quest from Nathos yet.
3) If needed, grind Honorbound reputation up to Honored 3000/12000.
4) Triggering the actual quest can be done in two ways: Getting reputation with Honorbound past the required rep (for example by doing a WQ on Kul'Tiras) or by relogging in Orgrimmar.
5) Now you can turn in Operation: Water Wise and continue on with next step of the War Campaign.

For Operation: Bottom Feeder:
1) Continue on with War Campaign, up to and including To Be Forsaken.
2) Do not accept next War Campaign quest from Nathos yet.
3) If needed, grind Honorbound reputation up to Honored 7500/12000.
4) Triggering the actual quest can be done in two ways: Getting reputation with Honorbound past the required rep (for example by doing a WQ on Kul'Tiras) or by relogging in Orgrimmar.
5) Now you can turn in Operation: Bottom Feeder and continue on with next step of the War Campaign.

For Operation: Hook and Line:
1) Continue on with War Campaign, up to and including With Prince in Tow.
2) Do not accept next War Campaign quest from Nathos yet.
3) If needed, grind Honorbound reputation up to Revered.
4) Triggering the actual quest can be done in two ways: Getting reputation with Honorbound past the required rep (for example by doing a WQ on Kul'Tiras) or by relogging in Orgrimmar.
5) Now you can turn in Operation: Hook and Line and continue on with next step of the War Campaign.