Even so, the decision by OKL to support the strategy in Directive 23 was instigated by two considerations, both of which had little to do with wanting to destroy Britain's sea communications in conjunction with the Kriegsmarine. First, the difficulty in estimating the impact of bombing upon war production was becoming apparent, and second, the conclusion British morale was unlikely to break led OKL to adopt the naval option. The indifference displayed by OKL to Directive 23 was perhaps best demonstrated in operational directives which diluted its effect. They emphasised the core strategic interest was attacking ports but they insisted in maintaining pressure, or diverting strength, onto industries building aircraft, anti-aircraft guns, and explosives. Other targets would be considered if the primary ones could not be attacked because of weather conditions.