Explanation: International radio regulations, specifically those governed by the ITU and SOLAS convention, empower foreign governments to inspect ship radio installations to ensure compliance. * **A) When a ship visits a port for the first time:** While a ship may be subject to routine port state control inspections, simply visiting a port for the first time does not, by itself, indicate any issue with the radio installation. It's a normal administrative event. * **B) When the ship's station license cannot be produced without delay:** The license is proof of authorization to operate. Failure to produce it immediately suggests unauthorized operation, a significant violation that would definitely prompt an inspection. * **C) When operational irregularities are observed:** This indicates potential non-compliance with frequency usage, power limits, or communication procedures, directly triggering a need for investigation. * **D) When compulsory equipment is found to be inoperative:** Ships are required to carry specific radio equipment for safety (e.g., GMDSS). If essential equipment is non-functional, the ship is not compliant with safety regulations, making an inspection and potential detention highly likely. Therefore, simply visiting a port for the first time (A) is the least likely scenario, as it doesn't inherently suggest any regulatory non-compliance regarding the radio installation, unlike the other options.