I’ve been gaming out Allied responses to a France First strategy with a friend.
For the defense of Holland, Rain is obviously a major aid. If it Rains, the best Dutch defense is in one of the clear hexes in front of the 2 cities. Ahh, but then the Axis simply Ground Strike the Dutch INF, put a ZoC on each city, and overrun the now OoS INF - that’s no defense at all! Except, this all requires a lot of units to flip over, and a lot of high movement point units all correctly positioned in the key advance hexes - are there enough such units? 5 movers flip to take a 3rd hex in rain, and an overrun costs 4...but the best outcome for the Allies is flipped German units. How many ART (pre-positioned, perhaps) and Air, each halved by Rain, will they commit to ensure the demise of the INF? Also, in Rain, they can just make a regular Blitz attack on the INF, but they can’t move a second hex off a B result, so the INF has to be overrun to reach Rotterdam.
Now if the Germans have enough high MP units positioned on the Dutch border (stacks make the best target for surprise impulse Ground Strikes) to do all of the ZoC positioning, then the overrun, then take the 2 cities (a lot of assets req.), or the weather is Fine, then the Allies should defend Amsterdam and land troops in Rotterdam. Without Rotterdam, the Germans can only get a one hex attack on Antwerp. That is not impossible, but it entails at least some risk. So the 1939 Germans will often seek to invade Rotterdam when Amsterdam is defended. Then the Royal Navy has a say, hopefully with a 4 range Gladiator on a CV in the 4 box of the North Sea, giving about a 65% ish chance of whacking whatever Kriegsmarine task force tries this.
Because without Antwerp, the Allies can easily hold the Dyle line until the weather clears in M/A or even M/J and all the new British financed Char B1 and especially the 47mm AT guns can give Heinz and Erwin a bitter taste of their own medicine.
But when the Germans look at Holland, the one hex they most want to see the Dutch INF in is - Rotterdam.