Нам нужна защита.

Because Russian expresses need with a structure closer to To us, protection is needed rather than We need protection.

• мы = we (subject form, nominative)
• нам = to us / for us (dative case)

In Нам нужна защита, нам is in the dative because the thing needed is presented as necessary for us.

A very common Russian pattern is:

• Мне нужен... = I need...
• Тебе нужна... = You need...
• Нам нужно... = We need...

So this sentence is literally something like To us, protection is necessary.

Нужна is the short-form adjective meaning needed / necessary.

It changes to match the noun that is needed:

• нужен — masculine
• нужна — feminine
• нужно — neuter
• нужны — plural

Here, the noun is защита, which is feminine, so we use нужна:

• Нам нужна защита.

Compare:

• Нам нужен врач. = We need a doctor.
• Нам нужно время. = We need time.
• Нам нужны деньги. = We need money.

Because защита is the thing that is needed, and in this pattern that noun normally stays in the nominative.

So in:

• Нам нужна защита

the grammar is roughly:

• нам = to us
• нужна = is needed
• защита = protection

This is different from English, where we is the subject and need is the verb. In Russian, the sentence is built differently, so the noun being needed often remains nominative.

Yes. In the present tense, Russian usually does not say the verb to be.

So:

• Нам нужна защита

literally works like:

• To us [is] needed protection

The present-tense is is understood and omitted.

In the past or future, forms of быть can appear:

• Нам была нужна защита. = We needed protection.
• Нам будет нужна защита. = We will need protection.

Защита can mean several related things depending on context:

• protection
• defense
• safeguarding
• sometimes even legal defense or thesis defense, in other contexts

In Нам нужна защита, the most natural meaning is usually protection or defense.

Examples:

• защита детей = protection of children
• правовая защита = legal protection
• защита города = defense of the city

So the exact English word depends on the situation.

Yes, you can.

• Нам нужна защита = We need protection.
• Мы нуждаемся в защите = We are in need of protection / We need protection.

The difference is mainly in style and structure:

Нам нужна защита

• very common
• simple and direct
• uses the dative + нужен/нужна/нужно/нужны pattern

Мы нуждаемся в защите

• more formal or bookish in many contexts
• uses the verb нуждаться в = to be in need of
• requires в + prepositional case, so защита becomes в защите

For everyday speech, Нам нужна защита is often the more natural choice.

Yes. Russian word order is flexible, and changing it can affect emphasis.

The neutral order here is:

• Нам нужна защита.

Possible variations:

• Защита нам нужна. — emphasizes protection
• Нужна нам защита. — can sound more expressive or contrastive

All of these can mean basically the same thing, but the neutral, standard version for learners is Нам нужна защита.

A good clue is the ending -а.

Most Russian nouns ending in -а or -я are feminine, including защита.

Because it is feminine, the short-form adjective must also be feminine:

• защита → нужна

Compare:

• план (masculine) → нужен план
• помощь (feminine) → нужна помощь
• место (neuter) → нужно место

So the form of нужен/нужна/нужно/нужны is a useful clue to the gender and number of the noun.

The stress is:

• нам нужнá защитa

More specifically:

• нам — one syllable
• нужнá — stress on the final -а
• защитá — stress on the final -а

So both нужна and защита are stressed on the last syllable.

A rough pronunciation guide:

• нам ≈ nahm
• нужна ≈ noozh-NAH
• защита ≈ zuh-shchee-TAH

The щ sound is softer/longer than English sh.

Yes, depending on context.

Because Russian does not have articles like a or the, защита by itself can be understood in different ways:

• We need protection
• We need defense
• sometimes We need a defense

The situation tells you which English wording is best.

For example:

• In a military context: We need defense
• In a personal safety context: We need protection
• In a legal context: possibly We need a defense

Yes. Необходима means necessary / essential, and it sounds stronger or more formal than нужна.

Compare:

• Нам нужна защита. = We need protection.
• Нам необходима защита. = Protection is necessary for us. / We absolutely need protection.

So both are correct, but необходима often sounds more serious, formal, or emphatic.