The easiest way to subscribe to a public calendar (like ours) is the copy and paste the calendar's ical address (https://www.google.com/calendar/ical/f1s47oika8v55etgg8gk766ous%40group.calendar.google.com/public/basic.ics) and email it to yourself. Then when you open the email, click the link. Your iPad or iPhone should ask if you want to subscribe to the calendar. Accept and you're all set.
If this option doesn't work for you, try the next option.
If that doesn't work, try these steps. These instructions largely came from this blogger's work.
Step 1: Copy the calendar's ical feed.
Step 2: Open Settings on your device and select "Mail, Contacts, Calendars"; then choose "Add Account..."
Step 3: Choose "Other"
Step 4: Paste the ical address
Step 5: Save the subscription and you're set.
Step 6: Go back to your main Calendar page and see if it shows up.