A bribe to prevent Israel from protesting too loudly?

Germany is providing Israel with a sixth Dolphin class submarine, at a discount of 135 million Euros. Why the discount? Here's a report that suggests that the discount is a bribe to convince Israel not to protest too loudly against German trade with Iran. And that it's not the first time it's happened. One theory is that Germany "donated" the first two after it was discovered in Israel that the