Situation ethics is used to mean the following; there is no ethical standard that can be consistently or uniformly applied. This is because each situation always demands its distinct standard of ethics. Utilitarianism is the effort aimed at providing answers to the day to day practical questions i.e. what does a man ought to do? The required conduct of any man is that they ought to act in a way so as to produce the best result possible out of any undertaking or activity.
A good example from which we can explore more on these two topics is the dropping of the atomic bomb on Japan's soil by the American's. This occurrence attracted debate with the argument that the course of action was unnecessary. However, the people of Japan were also working at developing a weapon that was similar. The weapon would be used against the American people unless intervention measure was taken. The bombing of Japan saved many Americans from consequences that would otherwise be regretted. The action helped America build a reputation during this war which actually forced many other nations to be afraid of what America was capable of doing. Although they killed many people from Japan, this was in exchange for the better good of the larger amount of people.
The prevailing condition led to the action that would be seen as unethical and in contravention of the international laws. Situation ethics however demanded that such an action is necessary for the good of the fair majority.
Utilitarian ethics for this very same case is also put to use. Ethics is a tool to be used for the good of masses. When the security of the people is threatened it is ethical to protect them in the best way possible. Unlike situation ethics that served to deal with the circumstances (the planned attack on America), utilitarian ethics was used because the American forces were under obligation to defend the interests of the American people. They therefore had to act in the way they did.