The St. Lo mission is an urban variation on the usual COH1-Normandy theme: You command a tiny US force at the outset, and you face a dug-in Wehrmacht force that vastly outnumbers and outguns you but is relatively static so you can defeat it in detail.
Here is a strategy that works reliably:
TAKE OUT THE ROCKET BATTERY
You start with a jeep and a handful of rifleman squads, and your intended base area is within range of three small German nebelwerfer units, which are heavily defended by HMGs and multiple infantry squads.
Use one low-strength rifleman squad to establish a garrison in the building closest to where your initial force appears. When the garrison is established, bring in an engineer team and use it to build a barracks, supply yard, and tank depot. Initially this construction will be harassed by nebelwerfer fire, especially at the north end of the base area, but that should end soon.
While you establish garrison and base, your other rifleman squads, after hanging back until the initial nebelwerfer barrage is finished, should move out in a wide flanking route to the right of the nebelwerefer battery and then in from behind it. The jeep can take a different route—it won’t last long or do anything to the Germans but it will draw some HMG fire away from the riflemen. The riflemen collectively should be able to get in a few grenade tosses before they are pinned by HMG fire and forced to retreat. Reinforce at the base, and repeat until the rocket launchers are de-crewed.
As soon as the nebelwerfers are silenced, you will get reinforcements consisting of a Sherman and a croc, plus a jeep and two Ranger squads.
TAKE THE NORTHWEST SIDE OF THE MAP
You get the mission medal by vetting one of the Ranger squads (or any other Rangers you bring in with the commander ability) up to vet-3 level by the end of the mission. For me, this was the most difficult of the medals in the Normandy campaign, because the Rangers are way too fragile—also not impressive in terms of firepower—to survive for long against the over-buffed Wehrmacht units. If you’re not going to bother about the medal, suicide your Rangers and use that freed pop cap for tanks. (Four tanks, a croc, a couple of engineer teams, call-in artillery and maybe a captured nebelwerfer or two are all you really need on this map.) If you do want the medal, you’ll need to make sure at least one of your Rangers is in on multiple tank-kills. Be sure to build a medic station near your retreat point.
Now that you have armor, use it to take out the units around the de-crewed rocket-launchers, plus the two snipers in buildings at the lower left corner of the map, and the Ostwind near them. Re-crew at least a couple nebelwerfers.
Note that pathing bugs occur in the area around the nebelwerfers. Your units might be unable to recrew one or more nebelwerfers, or they might exit a building to a position where they are stuck with no way out. Tanks running nearby and breaking stuff can sometimes fix this.
Next, move methodically, un-hurriedly up the NW or left side of the map (staying outside the central German base) led by your armor since the Germans have MG42s everywhere. You will also encounter Panzer IVs, Pumas, StuG IVs, schreck infantry, stormtroopers, ordinary grenadiers and volksgrens, Pak-38s, and mortar teams. Often the biggest challenge is bringing enough firepower to bear on German units in the close confines of this urban map. Call-in artillery or your nebelwerfers can help with that.
When you have destroyed all German units and taken all points on the NW side of St. Lo, set up defenses against German infantry and armor that will occasionally materialize on the road entrance at the top corner of the map. You can lay double rows of tank traps, plus wire and (at a distance) HMG bunkers for infantry.
TAKE THE REST OF THE MAP
Move methodically across the area above the German base, terminating every German unit and capping every point, until you reach the open plaza. You may notice that some German units materialize behind you occasionally. The magic of Relic!
Keep your softer units, like the nebelwerfers, guarded at all times. German units will race out from their base to kill any valuable but insufficiently defended unit.
Once you reach the plaza, you might face some counterattacks coming out from the base. Once those have quieted down, heal up and reinforce. Consider nuking the German base with some nebelwerfer salvoes.
Leading with a Sherman and a croc, head down the SE side of the map. You will quickly reach a heavily fortified area with multiple Paks and HMGs or grenadiers in every building. Use indirect fire here initially, and a croc to mop up. When the area is clear, cap the point.
Now move down to the next area, which has a bunker-like German base building and a Pak (facing south, away from you), and again use indirect fire and your croc, plus an ordinary Sherman if needed, to wipe everything. When you take that point, it closes the ring around the city for the win, and you never have to bother with all the German units at the bottom of the map.
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