Montgomery's ill-fated operation to capture the Rhine crossing at Arnhem was ingenious but fatally flawed. Evidence suggests that the Allies knew there were German armoured units in the town a few days before the first paratroopers landed, so why send them? The paras had no effective anti-tank weaponry and so surely it was suicide to carry out the original plan.
Here are details on the incident from Wikipedia:
Another source states that:
So, there was intelligence on the Nazi armoured divisions. The article goes on to say that:
So, Browning was the cause of this mistake. Here is another excerpt from Wikipedia.
There are a few possible reasons for this.
If the British had heeded word from their agents in Arnhem, they would have been alerted to the presence of two enemy panzer divisions.
This one played the bigger role of the two. The allied commanders believed that the Germans were still retreating in an unorganized fashion and were incapable of putting up an effective resistance. This made them believe that the airborne corps would meet little resistance. Otherwise, they might have paid more heed to the reports of German armour. The allies correctly believed the Germans had about 50 tanks. What they did not take into account however, was that, "the soldiers crewing these tanks were some of the best in the Wehrmacht". Also, the panzer strength was growing daily, because of superb German logistics. The allies were able to put together a "fairly coherent picture of German equipment strength, as of 01 September." However, by the 17th of September it had completely changed. Intelligence analysts vastly underestimated the recuperative ability of the German logistical reinforcement system.
The 10th PZ Division was under orders from Berlin (OKW) to handover its heavy weapons and to load and leave by train by Sept 13th. So the remaining kampfgruppe Harzer (2500 men) had almost no tanks available. Contrary to the orders its halftracks of the Panzergrenadiere were not all shipped to Germany or handed over to the 9th PZ Div near Ruurlo. The 9th PZ Div went into action near Nijmegen. After the landings both divisions were reinforced from Kleve with tanks wich happened to be underway to Aken.
My favorite sources are the book from Middlebrook and the site Defending Arnhem
My inkling is that through Ultra the OKW order to leave was known and all else was handed by the Germans by Phone and therefore not not decoded. We know that much about Ultra was never revealed. In those days long after the Englandspiel Dutch reports were daily and reliable again. In this case they were ignored.