Japanese signals intelligence and the exceptional failure at Midway

Were the Japanese as poor as Germany at signals intelligence, or even worse against the US Navy?

No. Japan was usually competent and security-conscious; its repeated failure to challenge the conspicuous American signals before Midway was exceptional.

Japan was generally capable in the intelligence war and normally showed appropriate suspicion. The open American messages about Midway's water system should have appeared too convenient because encoding them would not materially delay repairs or resupply. A cautious intelligence staff should have considered deception and the operational consequences of revealing an island's logistics problem. Midway therefore stands out as an unusual series of Japanese intelligence failures rather than normal practice.