Session 6 - Is a nuclear bomb an offensive or defensive weapon?

Robert Jarvis in his book "cooperation under the security dilemma" gives a realist view of what are the causes of wars and what can be done to reduce wars by for example by giving factors that makes cooperation among states more likely and a defect less likely. However I find a certain problem in his 'defense offence balance' theory.

The problem is that in today's world many of the weapons used in offense are also those that are used in offense. Meaning the same weapon can either be an offensive weapon or a defensive weapon based on whatever the state wants to interpret it as. So then how can anyone guess the states intentions by looking only at the weapons. Thus an aggressive and offensive looking  state looking to go to war can say it is building hundreds of fighter aircrafts (or maybe even a nuclear war) as a deterrent and to protect itself from an aggressor. Is such a weapon supposed to be classified as an offensive weapon or a defensive weapon? According to Jarvis, my example above would be of an offensive weapon because he says "Does the state have to spend more or less than one dollar on defensive forces to offset each dollar spent by the other side on forces be used to attach?" But this can be argued by the state claiming it is only building these weapons to defend itself and as a deterrent and not to attack anyone and so these weapons should be defensive weapons.

I agree with Jarvis's theory and all that he says is realistic. But it all comes down to interpretation and who does the interpretation. A superpower can say it is building so and so equipment to protect itself and its allies when in fact that same equipment can be used much more effectively and cheaply offensively. Who will argue with the superpower to say it is wrong. This is the problem.