The best way to check our work is to use the a values to draw the pieces.
This won't happen in the finished game so I created a test() function and added it to my functions.js.

function test() {
  for (id=0;id<100;id++) {
    var el=document.getElementById(id);
    var a=el.getAttribute('a');
    el.src='images/right/'+a+'.png';
  }
}

And this is what my index.html looks like right now:

<html>
<head>
<title>Ships</title>
<link rel='stylesheet' href='styles.css'>
<script src='library.js'></script>
<script src='functions.js'></script>
<script src='squares.js'></script>
<script src='seed.js'></script>
</head>
<body>
  <script>squares(); seed(); test();</script>
</body>
<html>
add this to functions.js for later
function get_a(r,c) {
  var id=rc2id(r,c);
  var el=document.getElementById(id);
  return el.getAttribute('a');
}